heat-db-setup doesn't support rhel7

[Ethan Lynn]

In rhel7 mysql-server is not an available package, instead, 'mariadb-server' is the default mysql backend in rhel.
When heat-db-setup is trying to install mysql-server, will fail with "'mysql-server' is not an available package" error.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/136763

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/136763
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=140f32805c28c62300fb3f8a1bd004b5db3d7442
Submitter: Jenkins
Branch: master

commit 140f32805c28c62300fb3f8a1bd004b5db3d7442
Author: Ethan Lynn <email address hidden>
Date: Wed Nov 26 10:35:46 2014 +0800

    Fix package name when using heat-db-setup in rhel7

    In rhel7 mysql-server is replaced by mariadb-server, using
    the right name to install package.

    Closes-Bug: #1395726
    Change-Id: I02e79a6f8da5bd082568c22d3efc4c231dfbd8c7