Fixes to make_javadoc.sh script

Three changes:

1. `BROOKLYN_VERSION` annotation to ensure that 0.7.0-SNAPSHOT reference is updated.
2. Javadoc output spews out a lot of noise to stdout and errors/warnings to stderr, but use of `tee` saves only stdout noise and not the useful error messages - changed to send errors to stdout, and what was stdout goes to /dev/null.
3. Abort if the required brooklyn-all-dependencies jar file has not been built.