[logging] log system time and mock time
Summary:
Currently, if mocktime is set, the logs will be timestamped with the mocktime instead of the system time. It's often useful to have the system time in the logs (for example, when running an integration test, it's useful to know what bitcoind was doing at system time so you can see how it's interacting with the test framework or other bitcoind nodes). This PR timestamps the log with the actual system time, and also prints out the mocktime if mocktime is being used.
Backport of core PR10383
Depends on D2422
Test Plan:
./test/functional/test_runner.py --nocleanup rpc_uptime
Check in the debug.log that both system time and mock time are logged
Reviewers: #bitcoin_abc, deadalnix, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Subscribers: teamcity, schancel
Differential Revision: https://reviews.bitcoinabc.org/D2423