ethereum: prevent unnecessary additional requests

[benjamincburns]

Web3 has recently added features that lazily fetches missing information
when signing and sending transactions. In our case, this was the
chainId, and the current gasPrice. Because transactions are submitted
asynchronously, these additional requests would sometimes cause
transactions to be submitted out of order. Even if this probelm were
mitigated, these additional requests added spurious latency spikes to
some transactions, negatively impacting the test results.

This partially addresses #776 by eliminating request reordering issues
for stable websocket connections. This change does not however address
transaction reordering for HTTP connections, or for websocket
connections that require reconnects. It also does not solve the
"christmas tree light" issue w.r.t. nonce errors.

[shemnon]

LGTM

[benjamincburns]

I spent most of yesterday testing out this patch and it seems to fix most of the problems we've observed (but only when using a websocket connection). Prior to this change, if we set the transaction send rate too high, we'd see a bunch of errors coming back. Now it works as you'd expect - there aren't any errors when the send rate is set higher than the chain can accept, and the tool reports the actual TPS. Personally I wouldn't trust benchmarking results from Caliper versions prior to this change, as they're very likely under reporting on performance.