Add support for vlan splinters

Add option use_vlan_splinters to site.pp. If enabled and osfamily is 'RedHat'
 then vlan splinters will be enabled if the driver for an bridge interface
 is present in the devices list in l23network::l2::splinters.

This behavior is disabled by default as not all installs may suffer from this
 and should only be enabled when necessary.

Testing status: testing WIP
To test, change guest network controller to one of the drivers listed in splinters.pp (ie e1000)