Setup MySQL root password

Generate these passwords:
  OVERCLOUD_MYSQL_ROOT_PASSWORD
  UNDERCLOUD_MYSQL_ROOT_PASSWORD

This change depends on I6d38ca82c77a4aa8f58089c50aa5bf320ec0ecc6
landing first.

Change-Id: I41698115c46f253f2ad06c44a6588ef1f67a7dbe
Merge "Setup MySQL root password"