Application containers with libvirt lxc driver

Existing libvirt lxc driver implementation only supports running a full OS containers.
The aim of this blueprint is to enable the users to run applications in an isolated container,
directly from the host filesystem, without the need of providing an OS image.
Avoiding the need, of having an image, will eliminate the need of copying it between hosts and
will reduce the I/O performance overhead, caused but various layers, which are mounting the image.

Users will be able to provide a set of Glance image properties to enable the above behaviour.

lxc_init_path - Sets the path to an application that would be launched in the container.
                May also be provided with a full OS image to serve as an alternative init
                command.

lxc_root_source_dir - Should be set to true, in order to launch the application from the host fs.

glance image-update \
           --property lxc_init_path=/sbin/sh \
           --property lxc_root_source_dir=true \
           [image]