Allow a property to control location of tzdb.dat file

Submitter would like either an environment variable or a system property to control the path to tzdb.dat.

Currently jdk8u and 9 both have pre-set path and would like to be able to override the calculated location of that file with a system property.

Current path is hardcoded in JDK :

            String libDir = System.getProperty("java.home") + File.separator + "lib";
            try (DataInputStream dis = new DataInputStream(
                     new BufferedInputStream(new FileInputStream(
                         new File(libDir, "tzdb.dat"))))) {
                load(dis);