Skip RPC selection step

[czepluch]

For the DappNode package, we want to be able to either hardcode or skip the RPC selection step, since dappnode offers it's own RPC endpoint and being asked to provide an Infura endpoint goes against the mission of DappNode and decentralizing Ethereum in general.

On request by @eduadiez the 3 arguments he'd like to be set are:

      - KEYSTORE_PASSWORD=
      - NETWORK_ID=mainnet
      - "RPC_ENDPOINT=http://fullnode.dappnode:8545"

[czepluch]

@eduadiez please chime in if you have any additions.