Add a plugin that permit to use ansible for lxc system, using libvirt

Using -c lxc and the domain name as hostname, this permit to manage a whole
range of container, provided they are managed and created by libvirtd.
add a inventory script that go with the lxc connexion module
Merge pull request #4064 from mscherer/lxc

Add a plugin that permit to use ansible for lxc system, using libvirt