[test] Add swarming option to numfuzz

This is added only to uniformly call all tools by the infra side.

NOTRY=true
TBR=sergiyb@chromium.org

Bug: v8:6917
Change-Id: I85a14ea51abfe1bfc775fd73d2fee02bfb2fb31e
Reviewed-on: https://chromium-review.googlesource.com/878361Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50754}

tools/testrunner/num_fuzzer.py

@@ -71,6 +71,9 @@ class NumFuzzer(base_runner.BaseTestRunner):
     parser.add_option("--rerun-failures-max",
                       help="Maximum number of failing test cases to rerun.",
                       default=100, type="int")
+    parser.add_option("--swarming",
+                      help="Indicates running test driver on swarming.",
+                      default=False, action="store_true")
 
     parser.add_option("--stress-marking", default=0, type="int",
                       help="probability [0-10] of adding --stress-marking "