RFR(XS): 8068778: [TESTBUG] CompressedClassSpaceSizeInJmapHeap.java fails if SA not available

[Lindenmaier, Goetz]

Hi,

This test uses SA, thus fails on platforms where that's not implemented.
I see problems on mac and aix.
Call Platform.shouldSAAttach() to check whether SA should work.

Please review this small fix.  I please need a sponsor.
http://cr.openjdk.java.net/~goetz/webrevs/8068778-jtregSA/webrev.01/

Best regards,
  Goetz.