os/ssh/mysql hardening roles from dev-sec

[martbhell]

dev-sec have some three nice hardening roles for os, ssh and mysql. The ssh one:

https://github.com/dev-sec/ansible-ssh-hardening

Maybe we can't use all but some good pointers perhaps and as we most likely only want to do some of the tasks - PRs/a fork to allow selecting what to enable/disable would be needed.