cbuildbot: add option to override committer email

It defaults to whatever is configured in git config which is @chromium.org
account for most people, which does not allow running remote buildbots for
people with unlinked accounts. This allows specifying @google.com account
which has rights to run remote buildbot.

BUG=none
TEST=cbuildbot --remote --committer-email=ldap@google.com -g \
randomchangefromgerrit samus-full

Change-Id: I4d24fb324ba741bb9ab6b357dcca7d7199aff154
Signed-off-by: Dominik Behr <dbehr@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/435547
Commit-Ready: Haixia Shi <hshi@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index d8b4685..9b11aa3 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -500,6 +500,8 @@
   group.add_option('--test-tryjob', action='store_true', default=False,
                    help='Submit a tryjob to the test repository.  Will not '
                         'show up on the production trybot waterfall.')
+  group.add_option('--committer-email', type='string',
+                   help='Override default git committer email.')
 
   parser.add_option_group(group)