Added support of resize-flavor to Redis datastore

trove resize-flavor was not supported for Redis;
If this command is indeed invoked, then the DB VM
would be stuck at the RESIZE state forever, as the
revert function (reset_configuration) is not implemented too;

This patch implements the resizing functionality for Redis

Change-Id: I93a1fe6e583636d72b8d399418d80bd124b36285
Closes-Bug: #1300477
Merge "Added support of resize-flavor to Redis datastore"