HPCC-8749 Support common directory for loading java classes

Regression suite tests for embedded Python/Java struggle because of classpath
issues.

Python case can be managed via a path on the IMPORT parameter (though it
should prepend rather than append the supplied path) but Java requires a
standard location to be selected up front.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #3936 from richardkchapman/embed-cleanup

HPCC-8749 Support common directory for loading java classes

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>