Removes `:install_options` from mariadb-galera-server install.

It turns out that the Puppet apt-get provider didn't even support
`:install_options` until version 3.6.0 [1] [2]. The
`DEBIAN_FRONTEND=noninteraction` option in particular causes an error
because apt-get interprets it as a command line option rather than as an
environment variable setting. Manually specifying this option also isn't
necessary because it is set in the environment when runing apt-get from
Puppet already [3].

[1]: https://tickets.puppetlabs.com/browse/PUP-772
[2]: https://github.com/puppetlabs/puppet/pull/2082
[3]: https://github.com/matthewbarr/puppet/blob/d9134621a7afd164a78c9ce895d7860400030e4f/lib/puppet/provider/package/apt.rb#L17