[tools] Add timestamps to each log line

We've originally added them in https://crrev.com/c/1159361 and then removed
again in https://crrev.com/c/1291370 since they were implemented in LogDog
Viewer. However, looks like logs from the swarming tasks are all dumped into
step stdout at the same time and thus logdog assigns idential timestamp to all
lines making it fairly useless.

TBR=machenbach@chromium.org

No-Try: true
No-Tree-Checks: true
Bug: chromium:841700
Change-Id: I49bfb23f8007e4a0facdfea6a09cde911f8e5a51
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1569432Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60875}

tools/run_perf.py

@@ -1015,7 +1015,8 @@ def Main(args):
 
   (options, args) = parser.parse_args(args)
 
-  logging.basicConfig(level=logging.INFO, format='%(levelname)-8s  %(message)s')
+  logging.basicConfig(
+      level=logging.INFO, format='%(asctime)s %(levelname)-8s  %(message)s')
 
   if len(args) == 0:  # pragma: no cover
     parser.print_help()