Add notifications to Munin and Slack notifier script

See also on dpla/aws#1
Could the email address come from a variable?  I'm not sure if the ones that already exist would work, so one might need to be created.  This would live in `ansible/vars/[ environment ].yml` or `ansible/roles/munin_master/vars/[ environment ].yml`; or perhaps even something like `site.yml` in that folder, with that file needing then to be included.  Whatever has the email address coming from a variable in the best way.