7141462: ProblemList.txt updates to exclude tests that cause test runs to hang [macosx]

[Alan Bateman]

Currently it's not possible to run some of the test targets that run the 
tests in agentvm mode, in particular the jdk_util and jdk_nio make file 
targets can cause jtreg to hang. I've looked briefly into these issues 
and see that there are at least three separate issues:

1. Asynchronous close of FileChannel operations as this is not fully 
implemented on Mac, in particular dup2 will hang if another thread is 
doing a blocking operation

2. A rouge test spins doing System.gc (this test is fixed in jdk8, just 
not back-ported jdk7u).

3. A strange hang loading libawt when Class.forName("<some-awt-class>") 
triggers the load.

In order to make some progress I would like the test that cause these 
issues to the ProblemList. All it means is that they excluded when 
running the tests via the Makefile. The webrev with the changes is here:

http://cr.openjdk.java.net/~alanb/7141462/webrev/

Thanks,
Alan.