tests: push with force in test_vcs_operations.py _add_files_and_push

Some tests push a fixed branch name. If such tests are run twice, it will fail
second time when the other branch head already exists.

Work around that by using force and thus replace the old head.

kallithea/tests/other/test_vcs_operations.py

@@ -158,9 +158,9 b' def _add_files_and_push(webserver, vt, d'
     # PUSH it back
     stdout = stderr = None
     if vt.repo_type == 'hg':
-        stdout, stderr = Command(dest_dir).execute('hg push --verbose', clone_url, ignoreReturnCode=ignoreReturnCode)
+        stdout, stderr = Command(dest_dir).execute('hg push -f --verbose', clone_url, ignoreReturnCode=ignoreReturnCode)
     elif vt.repo_type == 'git':
-        stdout, stderr = Command(dest_dir).execute('git push --verbose', clone_url, "master", ignoreReturnCode=ignoreReturnCode)
+        stdout, stderr = Command(dest_dir).execute('git push -f --verbose', clone_url, "master", ignoreReturnCode=ignoreReturnCode)
 
     return stdout, stderr