test: Add elapsed time to RPC tracing
Summary:
Add elapsed time to output of --tracerpc. To find out why tests are
slow.
Backport core's PR10352
Test Plan:
./test/functional/test_runner.py
Reviewers: #bitcoin_abc, matiu
Reviewed By: #bitcoin_abc, matiu
Subscribers: teamcity
Differential Revision: https://reviews.bitcoinabc.org/D1007