Added keep_ip flag for provider to move physical_interface IP to the bri...

This is a first approach to configure a network node while the IP from a physical interface is active and transferred over the bridge port.

Usage example:

vs_bridge { 'br-ex':
  provider => ovs,
  ensure   => present,
} ~> vs_port { 'external':
  bridge    => 'br-ex',
  interface => 'eth0',
  keep_ip   => true,
  provider => ovs,
  ensure   => present,
}