libvbucket: Substitute localhost marker in the config

This marker might appear since server release 2.5 as part of CCCP

More info:
* http://review.couchbase.org/29996
* http://review.couchbase.org/30067

This patch in libvbucket project: http://review.couchbase.org/30834

Change-Id: I2a27a89501dd72563f7aa7e7da911e174c4565a8
Reviewed-on: http://review.couchbase.org/30315
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>