python3: Add support for wlan device add

With this change it's now possible to add wlan devices to the container.
This will track down the right phy device, move it to the right
namespace (we don't care about its name), then if the user asked for a
new device name for the actual interface, we attach to the container and
rename the interface in there using attach.

I have tested this to work with both Intel and Atheros NICs.

This patch is based on the one provided to lxc-devel by Gregor Beck and
has then been updated to do the device renaming as well as minor code
style changes. Thanks!

Reported-by: Gregor Beck <gbeck@sernet.de>
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>