lxc_unshare -u argument useful even with USER namespace shared

Signed-off-by: Seth Robertson <srobertson@appcomsci.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Teach lxc_unshare about interfaces, mounts, hostname, daemonize

lxc_unshare now takes one or more '-i interfacename' arguments which
will move the named interfaces into the created container.

lxc_unshare now takes -M argument which will cause the standard mounts
(/proc /dev/shm /dev/mqueue) to be auto-mounted inside container.

lxc_unshare now takes '-H hostname' argument to automatically set
the hostname in the container.

lxc_unshare now takes -D argument to automatically daemonize and detach
from the created container, instead of waiting for the container to exit

Signed-off-by: Seth Robertson <srobertson@appcomsci.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>