lxcapi: Add new get_ips() call

This adds a new get_ips call which takes a family (inet, inet6 or NULL),
a network interface (or NULL for all) and a scope (0 for global) and returns
a char** of all the IPs in the container.

This also adds a matching python3 binding (function result is a tuple) and
deprecates the previous pure-python get_ips() implementation.

WARNING: The python get_ips() call is quite different from the previous
implementation. The timeout argument has been removed, the family names are
slightly different (inet/inet6 vs ipv4/ipv6) and an extra scope parameter
has been added.

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