Move MySQL settings out of puppet/controller.yaml

Move MySQL settings out of puppet/controller.yaml

This moves the config settings out of controller.yaml for MySQL
and into puppet/services/database/mysql.yaml.

The top leve MysqlRootPassword is still maintained by default
in overcloud.yaml so that users who upgrade won't get
broken. New users may optionally specify the MysqlRootPassword
as a parameter instead which will take priority over the top
level generated parameter.

We drop the top level MysqlClusterUniquePart because it is no
longer used (I think it was a remnant from t-i-e).

Related-Bug: #1604414

Change-Id: I06ebac0f4c87dabfccefb2e550a64650868c5b26