git cl upload: die when --no-squash has no commit-msg-hook.

Otherwise, the program continues, and an exception is printed.
The message is still there, but easy to miss.

R=andybons@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2004303003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300674 0039d316-1c4b-4281-b951-d872f2087c98

git_cl.py

@@ -2528,7 +2528,7 @@ class _GerritChangelistImpl(_ChangelistCodereviewBase):
       print 'git-cl: Added Change-Id to commit message.'
       return new_log_desc
     else:
-      print >> sys.stderr, 'ERROR: Gerrit commit-msg hook not available.'
+      DieWithError('ERROR: Gerrit commit-msg hook not installed.')
 
   def SetCQState(self, new_state):
     """Sets the Commit-Queue label assuming canonical CQ config for Gerrit."""