Improve cloudtop error message on git cl failure

R=gavinmak@google.com

Fixed: 280621923
Change-Id: I856dc1eb4f3fcd65906196b66f358b1dd413012e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5547690
Auto-Submit: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>

gerrit_util.py

@@ -511,7 +511,7 @@ def ReadHttpJsonResponse(conn, accept_statuses=frozenset([200])):
     # The first line of the response should always be: )]}'
     s = fh.readline()
     if s and s.rstrip() != ")]}'":
-        raise GerritError(200, 'Unexpected json output: %s' % s)
+        raise GerritError(200, 'Unexpected json output: %s' % s[:100])
     s = fh.read()
     if not s:
         return None

git_cl.py

@@ -6862,6 +6862,8 @@ def main(argv):
     dispatcher = subcommand.CommandDispatcher(__name__)
     try:
         return dispatcher.execute(OptionParser(), argv)
+    except gerrit_util.GerritError as e:
+        DieWithError(str(e))
     except auth.LoginRequiredError as e:
         DieWithError(str(e))
     except urllib.error.HTTPError as e: