[buildbucket] Print build url on command line with buildbucket.py

V8 uses buildbucket.py to trigger flake-bisect jobs on command line.
It's more convenient if the build url is shown.

Bug: 711249
Change-Id: I5737c6f3fd72b60517662e8a4808186d6acc71db
Reviewed-on: https://chromium-review.googlesource.com/1226912
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: smut <smut@google.com>

buildbucket.py

@@ -134,6 +134,10 @@ def main(argv):
   if args.verbose:
     print content
 
+  build_url = content.get('build', {}).get('url')
+  if build_url:
+    print 'Build triggered on: %s' % build_url
+
   return response.status != 200