JCBC-320: Catch ConcurrentModificationException also for Memcache
Buckets.

Change-Id: I86f1feaca2dfbdd5a80d6dfb46636dbd03045a01
Reviewed-on: http://review.couchbase.org/27066
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>