RFR: JDK-8030793: Update jprt.properties to release jdk9

[Erik Joelsson]

Please review these changes to make/jprt.poperties and 
hotspot/make/jprt.properties. I've just added a jdk9 configuration to 
JPRT and this change is needed for JDK 9 to start using it. This will 
solve the issue of requiring a jdk8 boot when building in JPRT.

In the hotspot version of the file, there is a lot of separate 
configuration for jdk7 and jdk8. I didn't dare touch this now and opted 
to just add the jdk9 version of these variables. I would guess that this 
won't be necessary however since hotspot won't be delivered to multiple 
jdk releases anymore?

Webrev: http://cr.openjdk.java.net/~erikj/8030793/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8030793

I'm still unclear on where the hotspot change needs to go and if I need 
a separate bug for it? My interpretation is that the root repo change 
should go to jdk9/dev and the hotspot change to jdk9/hs-rt and that 
since these changes are using separate routes, a separate bug should be 
used. I also assume that as a jdk9 reviewer, I will be able to push this 
myself (after review) to the hotspot repo.

/Erik