[tools] Add a log line when retrying runnables

TBR=machenbach@chromium.org, tmrts@chromium.org

No-Try: true
No-Tree-Checks: true
Bug: chromium:872257
Change-Id: I12a61a7e09ab240a9ee0f3e4a06f1190583075c9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1565894
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60824}

tools/run_perf.py

@@ -1124,6 +1124,8 @@ def Main(args):
                 attempts_left -= 1
                 if not attempts_left:  # ignore failures until last attempt
                   have_failed_tests[0] = True
+                else:
+                  logging.info('>>> Retrying suite: %s', runnable_name)
               else:
                 break