Clean up after failed gerrit cl description edits

If either the edit creation or edit publishing fail, we're left with
an unpublished edit hanging around. This can result in a follow-up
invocation of 'git cl desc' (e.g. if the user changes their mind, or
retries) will also fail. So, clean up after ourselves.

BUG=671091

Change-Id: Icfe53996acf2555b82be0695a3c86ebb8c50b936
Reviewed-on: https://chromium-review.googlesource.com/418449
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

gerrit_util.py

@@ -602,6 +602,7 @@ def DeletePendingChangeEdit(host, change):
 
 def SetCommitMessage(host, change, description, notify='ALL'):
   """Updates a commit message."""
+  try:
     assert notify in ('ALL', 'NONE')
     # First, edit the commit message in a draft.
     path = 'changes/%s/edit:message' % change
@@ -631,6 +632,16 @@ def SetCommitMessage(host, change, description, notify='ALL'):
       raise GerritError(
           'Unexpectedly received a 200 http status while publishing message '
           'change in %s' % change)
+  except (GerritError, KeyboardInterrupt) as e:
+    # Something went wrong with one of the two calls, so we want to clean up
+    # after ourselves before returning.
+    try:
+      DeletePendingChangeEdit(host, change)
+    except GerritError:
+      LOGGER.error('Encountered error while cleaning up after failed attempt '
+                   'to set the CL description. You may have to delete the '
+                   'pending change edit yourself in the web UI.')
+    raise e
 
 
 def GetReviewers(host, change):