java: import include/linux everywhere

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: use even more portable code to find JAVA_HOME

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: update test_ffi_java_types to be more portable

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>