PYTHON-830 - Fix bad uses of _get_wc_override.

Author: behackett

pymongo/database.py

@@ -780,7 +780,7 @@ def _create_or_update_user(
             opts["pwd"] = auth._password_digest(name, password)
             opts["digestPassword"] = False
 
-        opts["writeConcern"] = self._get_wc_override()
+        opts["writeConcern"] = self._get_wc_override() or self.write_concern
         opts.update(kwargs)
 
         if create:
@@ -890,9 +890,10 @@ def remove_user(self, name):
         """
 
         try:
+            write_concern = self._get_wc_override() or self.write_concern
             self.command("dropUser", name,
                          read_preference=ReadPreference.PRIMARY,
-                         writeConcern=self._get_wc_override())
+                         writeConcern=write_concern)
         except OperationFailure, exc:
             # See comment in add_user try / except above.
             if exc.code in common.COMMAND_NOT_FOUND_CODES: