Add --bootstrap-args option

Right now we can't test with remote trybot patches that add a new
option flag, because cbuildbot fails to recognize the new option.

To fix this, add a --bootstrap-args option, the value of which are not
verified by the remote bootstrap code, and directly passed to the
re-execution.

TEST=local testing
BUG=chromium-os:30710

Change-Id: Ibdf5d7df575b4cbcca64ab4b38985655eabf1865
Reviewed-on: https://gerrit.chromium.org/gerrit/23177
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: Ryan Cui <rcui@chromium.org>
Reviewed-by: Brian Harring <ferringb@chromium.org>
Commit-Ready: Ryan Cui <rcui@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index b19bfe1..1ff3f19 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -765,6 +765,10 @@
       'Advanced Options',
       'Caution: use these options at your own risk.')
 
+  # bootstrap-args are not verified by the bootstrap code.  It gets passed
+  # direcly to the bootstrap re-execution.
+  group.add_remote_option('--bootstrap-args', action='append',
+                          default=[], help=optparse.SUPPRESS_HELP)
   group.add_remote_option('--buildbot', dest='buildbot', action='store_true',
                           default=False, help='This is running on a buildbot')
   group.add_remote_option('--buildnumber', help='build number', type='int',