Replace FACTER_url with --resource for puppet device

Since 2012, we've used FACTER_url as a workaround for puppet resource:

A limitation to watch out for in the current Puppet release is that 'puppet apply' and 'puppet resource' cannot modify network resources. However, we implemented a feature to allow puppet resource to query a F5 device. (For authors of types/providers, making changes to resources aren’t supported until apply_to_device in resources type are handled differently by puppet apply/resource commands). For now we use url facts to establish connectivity to specific F5 devices.

https://puppet.com/blog/managing-f5-big-ip-network-devices-puppet

Using FACTER_url is insecure, as it places authentication credentials either in history or in the environment. It's also ugly.

If we implement --target in puppet resource as we've done in puppet device we can lookup the target device's url and internally set {{Facter(:url). This would not require changes to existing device modules.

If we implement this as a device(name) method in Puppet::Util::NetworkDevice::Config, it would allow device tasks to use device(name) to target devices.