RFR(M): 8047740: Add hotspot testset to jprt.properties

[Mikael Vidstedt]

All,

Please review the below change which adds a "hotspot" testset to the top 
level jprt.properties and makes it possible to do the equivalent of a 
hotspot push job but from the top level -- building the whole/full JDK 
but running the same old tests. The change should not change any 
existing use cases, so unless using the hotspot testset specifically 
everything should work exactly as it does today.

Bug: https://bugs.openjdk.java.net/browse/JDK-8047740
Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8047740/webrev.00/webrev/

Note that the name of the testset is used to control not only which 
platforms are being built and tested, but also whether a mercurial sync 
should be made after build/before push - specifically, the testset is 
"hotspot" handled differently from the other testsets.

I have manually verified that when running with the various testsets the 
build and test target sets are the same as before the patch.

Thanks,
Mikael