We want to be able to incrementally test the new movePrimary protocol as it's being developed, so let's add a temporary 'forTest' boolean flag to mongo's and the config server's movePrimary IDL definitions.

If the flag is set, configsvrMovePrimary should call movePrimary against the primary shard; otherwise, it should execute the existing movePrimary logic.

Add a jstest that calls movePrimary with the 'forTest' flag to ensure it's working.