Changed require mysql to include mysql::server in dashboard class.

Change-Id: Iacf0ef038e90faaacdb138b691f9c254bd3f5ad8
Reviewed-on: https://review.openstack.org/25287
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins