Create compatibility with new puppet mysql

[spuder]

puppet module mysql rewrote the mysql class, fix packages.pp line 238

https://forge.puppetlabs.com/puppetlabs/mysql

Also fix readme.md with new setup instructions

[spuder]

Fixed,

Gitlab now only works with puppet labs-mysql 2.0.0 or greater.
There are comments in init.pp and /tests/init.pp that explain how to roll back to the old syntax if needed.

Commit: bcbea0c [bcbea0c]