Make gateway, broadcast and dnsnameservers optionals

- Latest version of interfaces.template allows gateway to be optional
- dnsnameservers has always been optional
- broadcast shouldn't be required (can be computed if needed/missing)
- Add missing dnsdomain parameter to derivate classes of BaseOSUtils
- Use keyword arguments instead of positional arguments
- Improve logging of static network configuration
Add multi network interfaces support

We assume network interfaces configuration are sorted
in the desired order.

Known limitations:
- IPv4 only
- Static IP address only
Add support for dhcp and manual config methods

An administrator can override the template used by Nova
for network configurations injection.

This change adds support for dhcp and manual configuration methods.