First step towards automating releases (T663). This eliminates manually copy-pasting the blockhash + chainwork.
Prerequisite: You must have bitcoind running with --rest=1 set either as a CLI arg or in the config.
In the near future, we will have a dedicated node that can have these requests directed to (at that point,
the hostaddr default will change from localhost to that dedicated node).
Typical usage during a release is to replace mainnet params (update-chainparams.py with no args set).
Occassionally, testnet params need to be updated as well, and may be done with update-chainparams.py -t.
Both of these uses assume default node settings regarding rpcport, rpcusername, rpcpassword, etc.