EntityConfigResource, fix broken GET method

Also adds unit tests
BrooklynNode: classpath config updates

Changes type from List<String> to String, with semicolon separated URLs. getClasspath() method reads from brooklyn.properties if classpath is not configured on the entity.
AMP compatibility workaround

The brooklyn dist.tar.gz puts everything in a subdirectory called "brooklyn-VERSION". The AMP dist.tar.gz doesn't. This workaround checks for a "brooklyn-VERSION" directory; if it doesn't exist, it makes it a symlink to ".". This means that "brooklyn-VERSION/bin/brooklyn" will work for both brooklyn and AMP.