Add move change to Gerrit recipes

Will be used by a LUCI cron to move Gerrit changes for repos that are in
transition state #1 and #2.

R=ehmaldonado@chromium.org

Change-Id: Id7383ef677aa1cc90102c9a2aadbcc17712e150d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2522559
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

recipes/recipe_modules/gerrit/test_api.py

@@ -51,3 +51,8 @@ class GerritTestApi(recipe_test_api.RecipeTestApi):
 
   def get_empty_changes_response_data(self):
     return self._make_gerrit_response_json([])
+
+  def get_move_change_response_data(self, **kwargs):
+    change = EXAMPLE_CHANGE.copy()
+    change.update(kwargs)
+    return self._make_gerrit_response_json([change])