Inventory migration

[ahembree]

This moves variables from the vars/custom directory to the (hopefully) more correct inventory/group_vars/all directory.

This also requires the inventory file be recreated in yml format (personal preference) in inventory/hosts.yml.

This PR will add the following features:

• Ability to scale to multiple hosts since you will now be able to specify host-level variables in a custom inventory file
• Remove the need for the --connection local argument in the Makefile since the connection is now handled in the inventory file
• Additional make migrate-vars command to automatically copy the previous variable files to the new inventory/group_vars/all directory and create a symlink from vars/custom to point to the new location so the old directory will still work for now
• Removes unnecessary variable include task in the playbook since group_vars are auto-loaded
• Also adds sane-default for a variable used when deploying the custom monitoring scripts since this would usually error out in check_mode