cbdocloader should be killed if the bucket into which it is loading data is deleted (was: Loading and immediately deleting bucket leads to "Rebalance is not available until data loading is completed!" and cluster never comes out of this state)

1. Create a cluster of 4 nodes.
2. Load Travel-Sample bucket.
3. Still the data loading is in progress in the cluster and delete Travel-Sample bucket.
4. Observe that the cluster is stuck in “Loading Sample - Travel Sample” state and never comes out of this state.
5. Now Add/Remove Node, Rebalancing nothing works in cluster because “Warning: Rebalance is not available until data loading is completed!” And data loading will never complete because bucket is deleted. Although rebalancing operations is working through rest APIs but not thorough cluster UI console.

To get out of this, restart the memcached service is the only option left out.

Build: couchbase-server-enterprise_5.0.0-2873-ubuntu14.04_amd64.deb