decode and test for unlock cases of NOT_FOUND, NOT_MY_VBUCKET and ETMPFAIL

Current unlock implementation does not read the response and do anything with it. It simply says okay for any received responses.

Tests and implementation should check for the various responses expected. This should be documented somewhere and implementation should follow the documentation, but just to show what the current server implementation is I plucked this out of the server code for ep_engine:

ENGINE_ERROR_CODE rv = e->unlockKey(key, vbucket, cas, ep_current_time());

if (rv == ENGINE_SUCCESS)

{ *msg = "UNLOCKED"; }

else if (rv == ENGINE_TMPFAIL)

{ *msg = "UNLOCK_ERROR"; res = PROTOCOL_BINARY_RESPONSE_ETMPFAIL; }

else {
if (e->isDegradedMode())

{ *msg = "LOCK_TMP_ERROR"; return PROTOCOL_BINARY_RESPONSE_ETMPFAIL; }

RCPtr<VBucket> vb = e->getVBucket(vbucket);
if (!vb)

{ *msg = "That's not my bucket."; res = PROTOCOL_BINARY_RESPONSE_NOT_MY_VBUCKET; }

*msg = "NOT_FOUND";
res = PROTOCOL_BINARY_RESPONSE_KEY_ENOENT;
}