loader: Moving resolution of environment of cmdline args

Moving resolution of environment of cmdline args after networking has
been started to allow adding enviornment varilable that hold network
information (e.g. IP address).

Reviewed-by: Glauber Costa <glommer@cloudius-systems.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Shlomi Livne <shlomi@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>