[PRD-2488] fix horizon css file generation
Merge pull request #794 from Mirantis/prd2488

[PRD-2488] fix horizon css file generation
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.