Custom ChainStart Genesis Time Delay in Deposit Contract

[rauljordan]

This is part of #1565

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Description

Write why you are making the changes in this pull request

The specification for the deposit contract mentions how the genesis time is defined as 24 hours after the deposit threshold is reached. This is done to ensure nodes are all initialized and validators are ready to go for the beacon chain to begin. Currently, we use a flag called skip-chainstart-delay which instead sets the genesis time to time.Now(). The problem with this is that the beacon node needs time to initialize and validators need time to connect and prepare for the chain to begin. Given there is a discrepancy between when the log is initially fired and when validators are ready, validators may not begin their assignment until a few epochs have passed in the beacon node since genesis.

For example, below:

[2019-02-20 15:27:33]  INFO validator: Beacon chain initialized at unix time: 2019-02-20 15:27:03 -0600 CST
[2019-02-20 15:27:33]  INFO validator: Updated validator assignments attesterSlot=9223372036854775808 proposerSlot=0 shard=0
[2019-02-20 15:27:39]  WARN validator: Unknown role, doing nothing role=UNKNOWN slot=9223372036854775814 slotsSinceGenesis=6
[2019-02-20 15:27:45]  WARN validator: Unknown role, doing nothing role=UNKNOWN slot=9223372036854775815 slotsSinceGenesis=7
[2019-02-20 15:27:51]  WARN validator: Unknown role, doing nothing role=UNKNOWN slot=9223372036854775816 slotsSinceGenesis=8
[2019-02-20 15:27:57]  WARN validator: Unknown role, doing nothing role=UNKNOWN slot=9223372036854775817 slotsSinceGenesis=9

The validator begins at 6 slots since genesis because it received the chainstart genesis time too late from the beacon node.

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Instead of having a bool flag for skip-chainstart-delay in our contract, we could instead use a custom initializer parameter in seconds which we can use to customize the delay between when the chainstart log occurs and when the chain needs to begin based on the genesis time. This would allow us to set smaller values than 24 hours but greater than time.Now() for local testing of the the full ETH2.0 workflow.

[codecov]

Codecov Report

Merging #1666 into master will increase coverage by 0.22%.
The diff coverage is n/a.

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##           master    #1666      +/-   ##
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+ Coverage   70.82%   71.04%   +0.22%     
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  Files          97       97              
  Lines        6879     6846      -33     
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- Hits         4872     4864       -8     
+ Misses       1563     1543      -20     
+ Partials      444      439       -5