Provision users and databases on devserver-mysql role

Summary:
Salt uses the mysql execution module to configure MySQL, ie the pymysql
library. Credentials are stored in the node itself to use a localhost
root-like account "salt", defined in the pillar.

Test Plan: Deploy on db-B-001

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1803

Differential Revision: https://devcentral.nasqueron.org/D2987