RFR(S): JDK-8033926 Update hotspot/make/jprt.properties to use jdk9 instead of jdk8

[Staffan Larsen]

The first complete promoted build of jdk9 is now available and we can (finally) switch to using jdk9 in JPRT. Erik Joelson is currently updating the JPRT queues for jdk9. As soon as that work is done I will verify the proposed changes below by doing a complete JPRT run and then push the changes to hs-rt. The changes have already been tried out on the staging JPRT queue.

webrev: http://cr.openjdk.java.net/~sla/8033926/webrev.00

Thanks,
/Staffan