[TEST/REVIEW] Network discovery refactor/bugfix

This pull requests introduces the following changes:
* Removed the xsce_facts bash script
 * Use ansible_default_ipv4.device as xsce_wan_device
 * Search for first avaliable interface using ansible_facts and a template
* Added /etc/sysconfig/xsce_discovered_lan, so autodiscovery can be tested using 
    '''  ansible-playbook -i ansible_hosts --connection=local xsce.yml --tags=auto-discover '''
    And checking this file.

And allows for the following network configuration variables in vars/default_vars

xsce_lan_device:  # Auto-discovery, the default if omited
xsce_lan_device: "" # Force appliance mode
xsce_lan_device: "p7p1" # Use p7p1 as lan device