Make IO plugins depend on core for DEB

Change-Id: I8af0c364c87e230cba142a989a571d984700100b
Reviewed-on: http://review.couchbase.org/28373
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>