OBS-1499, OBS-1501 Refactor plays, add examples, and more

[mdpearson]

OBS-1490, OBS-1499 and OBS-1501 wound up being interrelated so I'm creating a big PR that resolves all three.

1. This PR should fix the issues @awalkowiak encountered with mysql not coming up cleanly the week before last.
2. It also refactors playbooks to remove PIH-specific code from them. Instead, things we need (like firewall rules and additional database users) are extracted from the inventory file. Folks who don't need this extra stuff just don't need to worry about it.
3. It also adds example inventory and vault files as a guide to help other sites configure their own installations.
4. It also prevents runaway disk usage by MySQL binlogs. We've only seen this with Oracle MySQL, although until now we didn't specifically turn it off on MariaDB.
5. While testing this on a clobbered obdev4 I noticed that reset_db.yml and restore_db.yml generate misleading logs when run on a host that hasn't had Openboxes deployed to it yet. That, too, has been fixed.
6. @jmiranda's request for a single playbook to update config has been granted.

I also added a lot more to the README.

[mdpearson]

This PR looks bigger than it is -- it's a lot of moving things around, which GitHub takes to be new code and deleted code.

That being said, it's a substantial refactor and I've tested it quite thoroughly, namely:

• clobbering obdev4 and obdev5 and bringing them up from scratch
• deploying from bamboo to a fresh host
• re-running the full runbook
• re-running just the configuration changes
• resetting the database before openboxes was deployed
• restoring the database before openboxes was deployed
• resetting the database after openboxes has been deployed
• restoring the database after openboxes has been deployed