containers: Sample program for driving container objects

Add a sample program to demonstrate driving a container object.  It is
called something like:

	./samples/vfs/test-container /dev/sda3

where /dev/sda3 holds an ext4 filesystem that has appropriate /etc, /bin,
/usr, /lib, /proc directories emplaced such that procfs can be mounted and
then /bin/bash can be executed within the container.

Signed-off-by: David Howells <dhowells@redhat.com>