Updated the locking semantics of lookUpOrCreateInodeIfNotStale.
Updated the locking semantics of lookUpOrCreateInodeIfNotStale.

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