We used to prefer creating a specific one for backups, but everybody
kept thinking the wrong key was being used and "fixing" it. The
advantages of having a specific key for backups did not outweigh
the challenge of creating a culture change.
Not just esthetic, for some reason ansible refused to run with '-'
somewhere and I just could not find where, changing variables and
tags to use '_' fixed it. It's more consistent anyway.
This makes it a bit more annoying to define default hosts for
multiple machines, but it's not that bad and it's better than not
being able to define heterogeous ports.