51517753: Publish JMeter reports to Sonar via Maven

Adds jmeter-maven-plugin to "jmeter" profile (invoke with "mvn <goal> -Pjmeter").
Adds a sample jmeter test plan to fcrepo-webapp/src/test/jmeter.

TODO: pull the latest fedora.jmx from ff-jmeter-madness on demand?

https://www.pivotaltracker.com/story/show/51517753