Add support for bridge interface type

- Example for configuration inside Vagrantfile:
  test_vm1.vm.network :public_network, :dev => "br0", :mode => 'bridge',
    :type => "bridge", :model_type => "e1000"
load missed module for 9p
Merge pull request #176 from stvleung/master

Fix destroy in vagrant 1.5.1+
Merge pull request #175 from mafigit/add_bridge_interface_support

Add support for bridge interface type
add module 9pnet_virtio