Otherwise this breaks git cl unit tests.

Update references to 'git cl' in git cl smoke tests to $GIT_CL.

TBR=ilevy@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/20888002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@214019 0039d316-1c4b-4281-b951-d872f2087c98