Add GET_MCPORTS mock command

This would be used for libcouchbase' testing with CCCP, to get the
proper CCCP ports

Change-Id: I8d3cfbfbad776b860fa83ec0a3215fa70a39ce78
Reviewed-on: http://review.couchbase.org/32499
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>