Add liblttng-ust-jul for JUL support

The build system creates a jar file named liblttng-ust-jul.jar to be
linked with the Java application. A public library named
liblttng-ust-jul.so is also created and must be in the library path of
the Java application in order for the LTTngAgent to use it for the
tracer's JNI call.

A unit test is also added and integrated with the "make check" command.

Signed-off-by: David Goulet <dgoulet@efficios.com>