assert on missing active validators' attestations when verifying finalization

[tersec]

Along the lines of #1386, but where that one shouldn't flag any conditions that wouldn't already (an epoch later) have triggered finalization failure, this tightens the requirements the 2/3 balance quorum, to being able not to receive only 10 of the testnet0/testnet1) 128 active validators' attestations. 8 of those will already come from some validators programmed not to attest, so that leaves a tolerance currently of 3 validators allowed not to attest without this firing.

So, this is quite a tighter check on the interactions between nbc and libp2p losing track of attestations in the context of justification and finalization.

Building: build/beacon_node
Building: build/deposit_contract
INF 2020-07-28 17:39:22+02:00 Generating deposits                        tid=343442 file=keystore_management.nim:107 totalValidators=128 validatorsDir=local_testnet_data/validators secretsDir=local_testnet_data/secrets
INF 2020-07-28 17:40:04+02:00 Deposit data written                       tid=343442 file=deposit_contract.nim:184 filename=local_testnet_data/deposits.json
Wrote local_testnet_data/network_dir/genesis.ssz
Wrote local_testnet_data/network_dir/bootstrap_nodes.txt
Wrote local_testnet_data/network.json:
{
  "runtimePreset": {
    "MIN_GENESIS_ACTIVE_VALIDATOR_COUNT": 128,
    "MIN_GENESIS_TIME": 0,
    "GENESIS_DELAY": 10,
    "GENESIS_FORK_VERSION": "0x00000000"
  },
  "depositContractAddress": "0x0000000000000000000000000000000000000000",
  "depositContractDeployedAt": "0x0000000000000000000000000000000000000000000000000000000000000000"
}
That was run #1
Building: build/beacon_node
Building: build/deposit_contract
INF 2020-07-28 17:48:53+02:00 Generating deposits                        tid=346112 file=keystore_management.nim:107 totalValidators=128 validatorsDir=local_testnet_data/validators secretsDir=local_testnet_data/secrets
INF 2020-07-28 17:49:34+02:00 Deposit data written                       tid=346112 file=deposit_contract.nim:184 filename=local_testnet_data/deposits.json
Wrote local_testnet_data/network_dir/genesis.ssz
Wrote local_testnet_data/network_dir/bootstrap_nodes.txt
Wrote local_testnet_data/network.json:
{
  "runtimePreset": {
    "MIN_GENESIS_ACTIVE_VALIDATOR_COUNT": 128,
    "MIN_GENESIS_TIME": 0,
    "GENESIS_DELAY": 10,
    "GENESIS_FORK_VERSION": "0x00000000"
  },
  "depositContractAddress": "0x0000000000000000000000000000000000000000",
  "depositContractDeployedAt": "0x0000000000000000000000000000000000000000000000000000000000000000"
}
That was run #2
Building: build/beacon_node
Building: build/deposit_contract
INF 2020-07-28 18:00:28+02:00 Generating deposits                        tid=350773 file=keystore_management.nim:107 totalValidators=128 validatorsDir=local_testnet_data/validators secretsDir=local_testnet_data/secrets
INF 2020-07-28 18:01:10+02:00 Deposit data written                       tid=350773 file=deposit_contract.nim:184 filename=local_testnet_data/deposits.json
Wrote local_testnet_data/network_dir/genesis.ssz
Wrote local_testnet_data/network_dir/bootstrap_nodes.txt
Wrote local_testnet_data/network.json:
{
  "runtimePreset": {
    "MIN_GENESIS_ACTIVE_VALIDATOR_COUNT": 128,
    "MIN_GENESIS_TIME": 0,
    "GENESIS_DELAY": 10,
    "GENESIS_FORK_VERSION": "0x00000000"
  },
  "depositContractAddress": "0x0000000000000000000000000000000000000000",
  "depositContractDeployedAt": "0x0000000000000000000000000000000000000000000000000000000000000000"
}
That was run #3

[tersec]

continuous-integration/travis-ci/pr failure at https://travis-ci.org/github/status-im/nim-beacon-chain/jobs/712622123 seems unrelated, since continuous-integration/travis-ci/push went fine on both platforms and continuous-integration/jerkins/branch both work fine:

/Users/travis/build/status-im/nim-beacon-chain/vendor/nim-confutils/confutils.nim(758, 23) Warning: Cannot prove that 'result' is initialized. This will become a compile time error in the future. [ProveInit]
\e[92mBuilding:\e[39m build/deposit_contract
\e[92mBuilding:\e[39m build/inspector
\e[92mBuilding:\e[39m build/logtrace
/Users/travis/build/status-im/nim-beacon-chain/beacon_chain/logtrace.nim(213, 19) template/generic instantiation of `decode` from here
/Users/travis/build/status-im/nim-beacon-chain/vendor/nim-serialization/serialization.nim(63, 31) Error: type mismatch: got <type JsonReader, InputStreamHandle, forwardCompatible: bool>
but expected one of: 
proc init(T: type JsonReader; stream: InputStream; mode = defaultJsonMode;
         allowUnknownFields = false): T:type
  first type mismatch at position: 3
  unknown named parameter: forwardCompatible
28 other mismatching symbols have been suppressed; compile with --showAllMismatches:on to see them
expression: init(
  JsonReader, stream`gensym36285275, forwardCompatible = true)
make: *** [logtrace] Error 1
make: *** Waiting for unfinished jobs....

[tersec]

continuous-integration/travis-ci/pr failure at https://travis-ci.org/github/status-im/nim-beacon-chain/jobs/712622123 seems unrelated, since continuous-integration/travis-ci/push went fine on both platforms and continuous-integration/jerkins/branch both work fine:

/Users/travis/build/status-im/nim-beacon-chain/vendor/nim-confutils/confutils.nim(758, 23) Warning: Cannot prove that 'result' is initialized. This will become a compile time error in the future. [ProveInit]
\e[92mBuilding:\e[39m build/deposit_contract
\e[92mBuilding:\e[39m build/inspector
\e[92mBuilding:\e[39m build/logtrace
/Users/travis/build/status-im/nim-beacon-chain/beacon_chain/logtrace.nim(213, 19) template/generic instantiation of `decode` from here
/Users/travis/build/status-im/nim-beacon-chain/vendor/nim-serialization/serialization.nim(63, 31) Error: type mismatch: got <type JsonReader, InputStreamHandle, forwardCompatible: bool>
but expected one of: 
proc init(T: type JsonReader; stream: InputStream; mode = defaultJsonMode;
         allowUnknownFields = false): T:type
  first type mismatch at position: 3
  unknown named parameter: forwardCompatible
28 other mismatching symbols have been suppressed; compile with --showAllMismatches:on to see them
expression: init(
  JsonReader, stream`gensym36285275, forwardCompatible = true)
make: *** [logtrace] Error 1
make: *** Waiting for unfinished jobs....

Fixed by #1389