RFR[9]: 8179084: HotSpot VM fails to start when AggressiveHeap is set

[Kim Barrett]

Please review this change to eliminate a VM startup failure when the
-XX:+AggressiveHeap option is used without a preceeding
-XX:ParallelGCThreads=<n> option.

In a debug build that configuration fails with:

#  assert(_initial_active_processor_count > 0) failed: Initial active processor count not set yet.

In a release build that configuration fails with java failing to
start, with a message of:
The Parallel GC can not be combined with -XX:ParallelGCThreads=0

So even the simplest of tests would have detected this problem.
Unfortunately, there are no tests in the jdk forest involving
-XX:+AggressiveHeap. This change adds a minimal test.

CR:
https://bugs.openjdk.java.net/browse/JDK-8179084

Webrev:
http://cr.openjdk.java.net/~kbarrett/8179084/hotspot.00/

Testing:
JPRT, including new test.
Locally executed new test with fastdebug and release builds:
- without change in fastdebug, verified the expected assert
- iwhtout change in release, verified the failure from the bug report
- with change in either, verified pass