[Telemetry] Add an option to log timestamp.
[Telemetry] Add an option to log timestamp.

With "--log_time" optional arg, we can see each logged event's
timestamp to know how long does a task spend.

BUG=None
TEST=manual ./run_benchmark with "-v --log_time" args added.

Review URL: https://codereview.chromium.org/1079443002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#330337}

benschmaus/catapult,benschmaus/catapult,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,sahiljain/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult-csm,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,SummerLW/Perf-Insight-Report,catapult-project/catapult-csm,sahiljain/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult