Added fix to support Couchbase resize-flavor

Implemented start_db_with_conf_changes and reset_configuration
operations for couchbase datastore.

Change-Id: I6e59b298bc28377e57659c0f2f80300f41937746
Closes-Bug: #1309317
Migrate v20 not handling exception

Version 20 upgrade creates 2 tables but the downgrade doesn't
remove them (for a stated reason). If you downgrade and then
upgrade, the upgrade will fail because the tables already exist.
This fix add a try block around the upgrade to log an info
message instead of failing.

Change-Id: I37fbe002da7dc764d229575149e4062e38f75881
Merge "Added fix to support Couchbase resize-flavor"
Merge "Migrate v20 not handling exception"