Fix for problems on metadata change with less nodes

1. Check for node existence in InvalidMetadataCheckingStore and
throw InvalidMetadataException if specified node is not in the cluster
2. Have ZenStoreClient rebootstrap when getting InvalidMetadataException.
This fixes if the new cluster does not have a node that ZenStoreClient query
data from, it would throw Exception.
Have update meta update store versions automatically
Add to EndToEndZoneShrinkageTest

1. Fixed ZenStoreClient NPE related to uninitialized sysStore
2. Added EndToEnd test for zone shrinkage to verify:
  a. Clients work correctly and rebootstrap in time after cluster change
  b. Slops does stream out correctly from dropping servers
  c. Slops targeting dropping servers get dropped
Update based on code review
Fix non static load method in ZoneShrinkageEndToEndTest
Updating release_notes for release 1.6.2
Fix KeyVersionFetcher to not depend on nodeid 0
Updating release_notes for release 1.6.3