javaunohelper: Enhancement loading bootstrap_parameters in Bootstrap_Test.java

Change-Id: I685fc278ec812d766ff83993d234ca3261a71dba
Reviewed-on: https://gerrit.libreoffice.org/10850
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>