lb: mark resources as array
rtpproxy: restructure rtpproxy_mi show command

Due to the initial structure, some useful information was stripped by the mi_json module.
Added the "Set" as root node, followed by a child for each node
Fixed missing \n in log messages.
Fix nameaddr.params if last param has no value.

Closes again #228 .
Fix ds_list MI command output.

The values added to the MI tree must be either persistent, either duplicated into the tree.
Closes issue #243, reported by Ovidiu Sas.
statistics: fixed MI get_statistics command to cope with mi_json