Handle primary IPs on devices and VMs

Add function to load YAML files ...

This commit starts to remove some code redundancy from the startup
scripts for easier maintenance.

Update Device Initializer for Netbox 2.7 ...

The device database model has changed in Netbox 2.7.
Therefore the initializer code, that was used before, broke.
As a user, you will need to update your devices.yml file as
follows:

- Make sure the rack face is spelled lowercase.

See the diff of this commit for further information how this is meant.

Add missing `break`

Fixed aesthetics.