packaging: support modifying java module path

if a customer need to have more recent version of module, he currently
have no way to apply except of replacing pre-installed files.

this change allows customer to add his own module path to search path to
shadow product modules.

Change-Id: Ibda53f67fa801cf4eb00b11483e9a6ab712d4d74
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>