lxc-ubuntu: Replace the hostname in ssh pubkey

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>
python3: Fix PEP8 and avoid crash when listing

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
python3: Drop duplicate add_device_node function

It is now natively implemented in C, the new function takes the same
arguments (same order, different names) and has been confirmed to work
with lxc-device.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>