RFR (XS): 8042804: Support invoking Hotspot tests from top level

[Mikael Vidstedt]

All,

Can I please get a review or two of the below change, which makes it 
possible to invoke/run the hotspot tests from the top level 
test/Makefile too - much like the jdk, langtools etc. tests. The 
implementation does this by simply delegating to the 
hotspot/test/Makefile - again, much like the jdk, langtools logic does.

* Bug:

https://bugs.openjdk.java.net/browse/JDK-8042804

* Webrevs

top: http://cr.openjdk.java.net/~mikael/webrevs/8042804/webrev.00/top/
hotspot: 
http://cr.openjdk.java.net/~mikael/webrevs/8042804/webrev.00/hotspot/webrev/

Thanks,
Mikael