Supporting arbitrary options

[chmduquesne]

This would solve #9.

Let me know if you are ok with this PR (in that case, integrate it). If you do not like it, I would just fork the role for my own use.

[tersmitten]

It looks like some option disappeared, am I right?

Can you describe if (or not) this is backwards compatible. Maybe using some examples?

[chmduquesne]

This supports arbitrary options, but this is not backwards compatible in the sense that in some cases, one needs to rewrite their variables if they want to achieve the same effect. So for example,

dns_search:
  - 8.8.8.8
  - 8.8.4.4

Becomes:

dns-nameservers: "8.8.8.8 8.8.4.4"

The idea is that options that would appear in an iface section (as in below "iface eth0 inet dhcp") are named directly after the option. This allows to support arbitrary options that were not possible before, and that I needed. For example, I am using this on my server now (note the "request_prefix" option)

network_interfaces_interfaces:
  - device: enp0s20
    family: inet6
    method: dhcp
    request_prefix: 1
    up:
      - "ip addr add {{ inet6_address }}/{{ inet6_netmask }} dev $IFACE"

It all boils down to the lines 13-17 in templates/etc/network/interfaces.d/device.j2.