Introduce combine_logs.py to combine log files from multiple bitcoinds.

Summary:
This commit adds a tool for combining log files from multiple instances
of bitcoinds as well as the test_framework.log file. This gives a
combined view of what the test framework and all bitcoin instances were
doing during a qa test.

Python functional tests should log in UTC

bitcoind logs use UTC. Python functional tests should also log in UTC.

Core Backport PR10017

Solves T141

Test Plan:
test/functional/test_runner.py
then, grab t A=<Temporary test directory>, and run:
test/functional/combine_logs.py $A/fundrawtransaction.py --color # for example

Reviewers: schancel, deadalnix, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1013