Deploy MySQL container for phpBB SaaS on Equatower

Summary: Root password is generated randomly for a new container.

Test Plan:

• salt equatower state.apply roles/paas-docker/containers
• run a MySQL client container linked to the MySQL server container

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1517