FindJNI: Unify path search, fix support for Java 9

Java 9 restructured the standard location of the AWT libraries due to
the removal of the JRE/JDK separation. We should check all possible
combinations of subdirectories to the Java root directories to ensure
that the libraries will be found after an upgrade.

Furthermore, a root directory would contain both, include and library
paths, so the search should be unified to ease maintenance on the
module.
Status Job ID Name Coverage
  External
passed ghostflow-check-master

passed ghostflow-stager