Support for external MySQL instances e.g. Cloud SQL

[andytheapedemontague]

The playbooks do not support the case of using a remote MySQL host, for example managed services such as Cloud SQL on GCP (and probably others such as Amazon RDS).

The playbook makes a bunch of assumptions that the MySQL server will be running on the Ansible controller node (and therefore the CS Cart server). Specifically:

• When specifying a remote host for the mysql group, the playbook sometimes fails due to a race condition with the installation of the packages. With the playbook running locally (-c local) and the MySQL server a remote host, Ansible will still try to run the MySQL package installation on localhost, but in parallel with other package installations leading to lock failures on the package manager.
• The mysql_* commands do not specify a login_host so default to localhost, which fails to connect to the remote host
• When setting the root password, the assumption is made that the login will be made from localhost. This is not true for remote MySQL hosts.

[andytheapedemontague]

PR fixing this attached.