python3: Add snapshot_* to the binding

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
python3: Allow setting daemonize and close_fds

This extends the list of arguments of start() allowing the user to
request the container be started in the foreground and have control on
whether fds will be closed or not (daemonize=True implies that too).

One problem at the moment however is that while we have functions to set
close_fds and daemonize in the API, we don't have functions to unset
those flags, so those new parameters will only work on the initial call
to start() any further call will use the values of the previous one.

I think it'd make sense to change lxcapi slightly to have daemonize and
close_fds offer a similar interface, both returning booleans and both
accepting a value as a parameter so API users can set the value they
want.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
python3: Use FSConverter for all paths

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