Fix threading bug in ReportCollectionFactory

The RemovalListener for a Gauva LoadingCache is run after the lock is dropped,
 so an expired object could be reinserted and re-registered before the removal
 listener could de-register it.

 Use additional data structures to detect this case and prevent the duplicate
 registration and subsequent deregistration.
Add back support for legacy http-client.threads config
Add back http-client.max-content-length configuration option

Max content length option was accidently removed during migration to new
JettyHttpClient.  The default value is still 16MB.
Add Hamcrest support to JsonTester
Create TestingReportCollectionFactory
Update CHANGES
[maven-release-plugin] prepare release 0.92
[maven-release-plugin] prepare for next development iteration
Expose JettyHttpClient stats via JMX
Check if fieldValue is null instead of fieldName
Revert "Add Hamcrest support to JsonTester"

This reverts commit a61531c965d17d458f9244af30ee4967007aa235.
Upgrade Jetty to 9.1.3
Workaround Cobertura incompatibility with Java 8
[maven-release-plugin] prepare release 0.93
[maven-release-plugin] prepare for next development iteration
Add default JVM options to launcher
Add IPv6 support to HttpUriBuilder
Convert values of type Descriptor to Map

The current code breaks with java 8 due to an mbean that has a nested descriptor in one
of its operation descriptors.
Always run rack servers in the "production" environment
No longer copy etc to rack/config