Poll-aroid abstraction

[mforhan]

As it stands the poll-aroid plugin has many hardcoded options for dealing with various plugins. Therefore, the core of the application needs to be abstracted to accept a generic --plugin= command option, and check the plugins directory for associated code. The plugin code should handle the RESTful query from the endpoint, leaving the core reporting metrics up to an output function which can work through a configuration file to report metrics in a way consistent to best practices. The best abstraction will allow a config file and an endpoint plugin to be added without changing the core code.