RFR(S): 8049071: Add jtreg jobs to JPRT for Hotspot

[Mikael Vidstedt]

Please review this enhancement which adds the scaffolding needed to run 
the hotspot jtreg tests in JPRT.

Bug: https://bugs.openjdk.java.net/browse/JDK-8049071
Webrev (/): 
http://cr.openjdk.java.net/~mikael/webrevs/8049071/webrev.00/top/webrev/
Webrev (hotspot/): 
http://cr.openjdk.java.net/~mikael/webrevs/8049071/webrev.00/hotspot/webrev/

Summary:

We want to run the hotspot regression tests on every hotspot push. This 
change enables this and adds four new test groups to the set of tests 
being run on hotspot pushes. The new test sets still need to be populated.

Narrative:

The majority of the changes are in the hotspot/test/Makefile. The 
changes are almost entirely stolen from jdk/test/Makefile but have been 
massaged to support (at least) three different use cases, two of which 
were supported earlier:

1. Running the non-jtreg tests (servertest, clienttest and 
internalvmtests), also supporting the use of the "hotspot_" for when the 
tests are invoked from the JDK top level
2. Running jtreg tests by selecting test to run using the TESTDIRS variable
3. Running jtreg tests by selecting the test group to run (NEW)

The third/new use case is implemented by making any target named 
hotspot_% *except* the ones listed in 1. lead to the corresponding jtreg 
test group in TEST.groups being run. For example, running "make 
hotspot_gc" leads to all the tests in the hotspot_gc test group in 
TEST.groups to be run and so on.

I also removed the packtest targets, because as far as I can tell 
they're not used anyway.

Note that the new component test groups in TEST.group - 
hotspot_compiler, hotspot_gc, hotspot_runtime and hotspot_serviceability 
- are currently empty, or more precisely they only run a single test 
each. The intention is that these should be populated by the respective 
teams to include stable and relatively fast tests. Tests added to the 
groups will be run on hotspot push jobs, and therefore will be blocking 
pushes in case they fail.

Cheers,
Mikael