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.
EntityConfigResource, fix broken GET method

Also adds unit tests