Skip apply_gerrit rebase when there is a rebase failure.

Not doing so causes a failure in the 'git checkout $base_rev' step as visible here: https://build.chromium.org/p/client.skia.fyi/builders/Infra-PerCommit-Trybot/builds/4995
This causes the checkout to remain in the "rebase in progress" state.

BUG=chromium:645955
BUG=skia:5749

Committed: 9736fe8938
Review-Url: https://codereview.chromium.org/2328313002

recipe_modules/bot_update/resources/bot_update.py

@@ -604,7 +604,12 @@ def apply_gerrit_ref(gerrit_repo, gerrit_ref, root, gerrit_reset,
       try:
         ok = False
         git('checkout', '-b', temp_branch_name, cwd=root)
-        git('rebase', base_rev, cwd=root)
+        try:
+          git('rebase', base_rev, cwd=root)
+        except SubprocessFailed:
+          # Abort the rebase since there were failures.
+          git('rebase', '--abort', cwd=root)
+          raise
 
         # Get off of the temporary branch since it can't be deleted otherwise.
         cur_rev = git('rev-parse', 'HEAD', cwd=root).strip()