Config Changes for thinning of Neutron Plugin

- Added extension code to handle neutron requests for network API
- config_db from neutron is moved to neutron_plugin_db.py in config-extensions
- neutron_plugin_interface.py handles the plugin API requests in cfgm
Schema changes for port api
get_network and get_network_count now use the /neutron/network URL
removed unnecessary bottle callbacks
Config/control node changes to support port changes
Added support in backend for subnet thinning
PR #2935 - (1) default argument specified in parser.add_argument() overwrites the values parsed from the conf file. (2) Fix package name specified in init_generator()
Fix build break and increase wait condition timeouts.
Fix analytics systemless test
Convert periodic logging of Collector list from Discovery to trace
Added sandesh.discovery package to opserver