Do not allow to use Administrator account for LCB_TYPE_BUCKET

Change-Id: Id0c46c55f164d730879b08e72b6a0104b354dce8
Reviewed-on: http://review.couchbase.org/28698
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>