add --ignore-submodules to apply_issue.py

Apply_issue should not try to check if there are modified files within submodules.

BUG=

Review URL: https://codereview.chromium.org/246093002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@265115 0039d316-1c4b-4281-b951-d872f2087c98

checkout.py

@@ -723,7 +723,7 @@ class GitCheckout(CheckoutBase):
       base_ref = '%s/%s' % (self.remote,
                             self.remote_branch or self.master_branch)
     found_files = self._check_output_git(
-        ['diff', base_ref,
+        ['diff', base_ref, '--ignore-submodules',
          '--name-only']).splitlines(False)
     assert sorted(patches.filenames) == sorted(found_files), (
         sorted(patches.filenames), sorted(found_files))