MySQL permissions and ansible

Created by: slifty

Running the ansible scripts to set up my local dev environment exposed a few little "gotchas" that I fell victim to, so I wanted to document them here in preparation for a PR.

1. The simplesaml ansible script requires a mysql_root_password setting that isn't currently in the template
2. I was using the default Debian version of ansible, which has a bug related to mysql permission granting. This is resolved in ansible 2.9 (thank you @frankduncan for the tip).
3. I was lazy and used the same username / password across different ansible scripts (e.g. when installing different competitions). Ansible will overwrite permissions by default, unless you explicitly set append_privs: yes

I have these changes locally, so would like to contribute them to the upstream.

(#87 (closed) talks about the root password issue as well)