RFR 8069286: Unexpected count of notification in LowMemoryTest

[Jaroslav Bachorik]

Please, review the following test change

Issue : https://bugs.openjdk.java.net/browse/JDK-8069286
Webrev: http://cr.openjdk.java.net/~jbachorik/8069286/webrev.00

In JDK-8034263 the conditions on the number of notifications were 
relaxed for the cases when running with CMS GC. Due to the nature of CMS 
we can assert only that at least the required number of notifications 
was fired. The fix omitted the fact that the assertion should be relaxed 
also on the gc count passed in the notifications. This patch takes care 
of the omission.

Thanks,

-JB-