gc/TestVerifySubSet.java is (sometimes?) failing on solaris sparc.

OutputAnalyzer reported
java.lang.RuntimeException: 'Threads' found in stderr

apparently because of this warning:

Java HotSpot(TM) 64-Bit Server VM warning: If the number of processors is expected to increase from one, then you should configure the number of parallel GC threads appropriately using -XX:ParallelGCThreads=N

which I *think* might be due to some interaction with this recent change: JDK-8185572 Enable AssumeMP by default on SPARC machines. The warning comes from code that tests AssumeMP, and would not have previously generated the warning if it were false.

Why we're getting only one thread is kind of mysterious, and that question came up in the discussion for JDK-8185572, and doesn't seem to have been resolved.