* Add Nagios livestatus inventory plugin.
* Add new capabilities for the nagios_livestatus inventory:
- host_field: set the name returned (default: 'name')
- group_field: set the field used for group (default: 'groups')
- host_filter: filter host using this filter (default: None)
To be more consistent, prefix was renamed into var_prefix.
* Fix py34 runtests errors against print call.
