Added tests verifying outputs for getblock rpc command

Summary: Added tests to verify output from the getblock (verbose) rpc command. Follow up to D2499.

Test Plan: test_runner.py rpc_blockchain

Reviewers: deadalnix, jasonbcox, Fabien, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, Fabien, O1 Bitcoin ABC, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2589