Add gclient_smoketest.py to PRESUBMIT.py check

It raises the time to run the presubmit to ~30 seconds but it's still worth.

TEST=run more often

Review URL: http://codereview.chromium.org/3146010

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@55759 0039d316-1c4b-4281-b951-d872f2087c98

PRESUBMIT.py

@@ -11,6 +11,7 @@ details on the presubmit API built into gcl.
 UNIT_TESTS = [
   'tests.gcl_unittest',
   'tests.gclient_scm_test',
+  'tests.gclient_smoketest',
   'tests.gclient_utils_test',
   'tests.presubmit_unittest',
   'tests.scm_unittest',