RFR 8034263: Test java/lang/management/MemoryMXBean/LowMemoryTest.java fails intermittently

[Jaroslav Bachorik]

Please, review the following test change

Issue : https://bugs.openjdk.java.net/browse/JDK-8034263
Webrev: http://cr.openjdk.java.net/~jbachorik/8034263/webrev.00

The test fails intermittently only for CMS collector -

"One thing about CMS is that it does concurrent work. So just a theory 
would be that a concurrent cycle is started and sometime finishes (which 
might trigger a notification) and sometimes does not finish before the 
test has completed. " (from discussion with Bengt Rutisson)

The 'fix' is to relax the condition for when CMS is used and check that 
at least the expected number of notifications was triggered.

Thanks,

-JB-