Port of wallet.sh to python (wallet.py).

Also included are minor edits to util.py to create a clean blockchain and add a parameter to gather_inputs to specify number of confirmations.
Edited rpc-tests to run python script not shell script.
Merge pull request #5333

e4ef724 Edited rpc-tests to run python script not shell script. (mrbandrews)
189fb52 Port of wallet.sh to python (wallet.py). (mrbandrews)