new debug command: toggles DEBUG log level

Signed-off-by: Guillermo Ontanon <guillermo@midokura.jp>
Resolve relative object refs

This commit add support for object refs to objects that
can only be found relative another one, in a child namespace.
Examples of this are refs to router and bridge ports, such as
those found in interface-to-port bindings.

Signed-off-by: Guillermo Ontanon <guillermo@midokura.jp>