The currently defined RabbitMQ Exporter probes make a call to the
"/metrics" path of the exporter service, which downloads a huge file and
takes a very long time to download. An http probe should be based on a very
simple and short url response from the service. So this changes the
probes to just call the base path "/" of the url and set the timeout to
something reasonable like 5 seconds.
Change-Id: Ie106490b2fb8d61660663f39a992bf4dc1a61222
72afe093aa