Download of plugins now makes use of Maven proxy info in settings.xml file

If you have never downloaded the form-element-plugin to your local maven repo AND
you are behind a HTTP proxy, then the download that is attempted during the test
will fail. This fix uses the maven proxy information if present in the settings.xml
file to permit the download.
Merge branch 'master' of github.com:scoheb/acceptance-test-harness

Conflicts:
	src/main/java/org/jenkinsci/test/acceptance/controller/AbstractJenkinsControllerFactory.java