mysql: Un-pin Puppetlabs MySQL module, update for >= 2.2

According a recent thread on puppet-openstack mailing list[1], we planed
to drop puppetlabs/mysql 0.x support for Juno release. Our module is
pined to 0.x branch because >= 2.2 break retro-compatibility. This
commit update puppet-openstack-cloud to the latest version of
puppetlabs/mysql.

[1] https://groups.google.com/a/puppetlabs.com/d/topic/puppet-openstack/8xJ-XtBa_C0