git cl try-results regression tests for Gerrit.

The flow looks like this:

  $ git cl status
  Branches associated with reviews:
    gerrit-4483 : https://chromium-review.googlesource.com/381231 (waiting)

  $ git cl try-results
  Warning: Codereview server has newer patchsets (2) than most recent
  upload from local checkout (None). Did a previous upload fail?
  By default, git cl try uses latest patchset from codereview,
  continuing using such patchset 2.

  Warning: Some results might be missing because You are not logged in.
  Please login first by running:
    depot-tools-auth login chromium-review.googlesource.com
  Started:
    Infra Linux Precise 32 Tester https://luci-milo.appspot.com/swarming/...
    Infra Linux Trusty 64 Tester  https://luci-milo.appspot.com/swarming/...
  Total: 2 try jobs

  $ depot-tools-auth login chromium-review.googlesource.com
   <<<auth in my browser>>>

  Logged in to chromium-review.googlesource.com as <some@email.com>

	To login with a different email run:
		depot-tools-auth login chromium-review.googlesource.com
	To logout and purge the authentication token run:
		depot-tools-auth logout chromium-review.googlesource.com

  $ git config branch.gerrit-4483.gerritpatchset 2
  $ git cl try-results
  Started:
    Infra Linux Precise 32 Tester https://luci-milo.appspot.com/swarming/...
    Infra Linux Trusty 64 Tester  https://luci-milo.appspot.com/swarming/...
    Infra Mac Tester              https://luci-milo.appspot.com/swarming/...
  Total: 3 try jobs

R=sergiyb@chromium.org,emso@chromium.org
BUG=599931
TEST=new unittests + end-to-end local.

Review-Url: https://codereview.chromium.org/2392463009
diff --git a/git_cl.py b/git_cl.py
index 381d8db..857bf37 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -4880,10 +4880,12 @@
                    cl.GetIssue())
 
     if patchset != cl.GetPatchset():
-      print('WARNING: Mismatch between local config and server. Did a previous '
-            'upload fail?\n'
-            'By default, git cl try uses latest patchset from codereview.\n'
-            'Continuing using patchset %s.\n' % patchset)
+      print('Warning: Codereview server has newer patchsets (%s) than most '
+            'recent upload from local checkout (%s). Did a previous upload '
+            'fail?\n'
+            'By default, git cl try uses latest patchset from codereview, '
+            'continuing to use patchset %s.\n' %
+            (patchset, cl.GetPatchset(), patchset))
   try:
     jobs = fetch_try_jobs(auth_config, cl, options.buildbucket_host, patchset)
   except BuildbucketResponseException as ex: