SPY-106: Allow GetAndTouchOperation to be cloned.

This fixes an issue where GAT called during rebalance, causing it
to be cloned potentially, fails the IO threads since its not
supported in there properly.

Change-Id: I3ff86456c5f2f28e206612890c08834fc96935f1
Reviewed-on: http://review.couchbase.org/29585
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>