Expect valid file descriptors ratio for *nix platforms
Merge pull request #387 from ceetav/metrics-387

Windows : JVM Integration for Metrics : FileDescriptorRatioGaugeTest failure
Give some love to metrics-jetty9.

* Removed InstrumentedConnector, as it provides no value.
* Made InstrumentedConnectionFactory lifecycle-aware, which fixes #389.
* Moved setup on most things to doStart, which closes #386.
* Added support for MOVE requests.
Add another quick test to metrics-jetty9.
Fix line endings for AdminServlet.

Closes #388.