RFR(S): 8159156: [TESTBUG] ReserveMemory test is not useful on Aix.

[Lindenmaier, Goetz]

Hi,

Another small test fix for Aix. Aix does commit on touch, i.e., the page is just
commited when this test wants to force an error.
So I just skip this test on aix.

I also adapted the other checks for OSes to use Platform.java.

Please review this change. I please need a sponsor.
http://cr.openjdk.java.net/~goetz/wr16/8159156-aixResMemTest/webrev/

I ran the test on ppc, linuxx86_64 and darwinintel.

Best regards,
  Goetz.