Declared implicit dirs tests for rmdir.
Declared implicit dirs tests for rmdir.

GoogleCloudPlatform/gcsfuse,kahing/gcsfuse,mbrukman/gcsfuse,BanzaiMan/gcsfuse,jacobsa/ratelimit,BanzaiMan/gcsfuse,GoogleCloudPlatform/gcsfuse,GoogleCloudPlatform/gcsfuse,jacobsa/timeutil