Fix GeoServerPersisterTest and the build

Makes the change described here:
http://osgeo-org.1560.x6.nabble.com/Build-failed-in-Jenkins-geoserver-master-600-tp5147692p5148268.html

Kevin, if you have time, please review
GeoServerPersisterTest.testModifyStyleWithResourcesAbsoluteChangeWorkspace;
it appears that this failure triggers the others (which pass when run
alone in Eclipse). @Ignoreing this one method makes everything pass. Is
the persister smart enough to find burg03.svg and copy it even via an
absolute file: reference? Could this reference instead be changed to
something like "http://doesnotexist.example.org/burg03.svg"? I am not
sure what you are testing here.