Add dns_name option for the Primary IP's dns_name host_var

[nahun]

Fixes #378. Adds the dns_name from the host's Primary IP to host_vars.

• Adds the dns_name option which forces IP addresses to be fetched and sets the dns_name host_var
• The interfaces option also causes IP addresses to be fetched, so the dns_name host_var will also be set with the interfaces option
• Added v2.10 fixes for the netbox_deploy.py script, but didn't fix all testing to work with v2.10. The inventory testing won't pass with v2.10
• I tested v2.9 locally and it passed. The automated testing will fail since it automatically gets latest from docker which is now v2.10.

[FragmentedPacket]

Thank you for adding this feature!

[spiglee]

Can we get some documentation examples put somewhere on how to use this? I'm still struggling when using NetBox as a dynamic inventory to make the connection using the DNS name rather than the IP. This is causing issues for me still with making a WinRM Kerberos connection.