Tests: Java agent: Add configure switches to enable tests

This patch adds the switches --enable-test-java-agent-(jul|log4j|all) to
the configure script, the tests now need to be explicitly enabled and
their dependencies are only checked if so.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>