Make rpc-probe create gaiad test fixtures

[greg-szabo]

rpc-probe currently runs against kvstore to create test fixtures. The preparations to do the same with gaiad (post-stargate) have finished. There is an informaldev:gaiad docker image to run and pre-populated transactions are available under tools/docker/gaiad-... that can create some traffic on a gaiad network so the endpoints return some richer results.

What needs to be done:

• Expand rpc-probe so it can run additional steps before it starts polling the endpoint:
  • Read the pre-signed transactions
  • Send them to POST 127.0.0.1:1317/txs (expect a gaiacli RPC endpoint there)
  • Note the height in the response
  • Use the height in the quiries where applicable to get a richer response (for example /block?height=...)

After this, the tendermint-rpc tests can be expanded with the gaiad fixtures for additional tests.