RFR(XS): JDK-8021774: [TESTBUG] Tests failed because of a warning in its output (backport fix for JDK8)

[George Triantafillou]

Please review the following fix for bug 8021774:

     JBS: https://bugs.openjdk.java.net/browse/JDK-8021774
     Webrev: http://cr.openjdk.java.net/~gtriantafill/8021774/webrev.00/ 
<http://cr.openjdk.java.net/%7Egtriantafill/8021774/webrev.00/>

This backport fix for JDK8 is a test stabilization change. The goal of 
the change is to ignore warnings with -XX:NativeMemoryTracking on 
Solaris and Linux in order to achieve a full pass of jtreg runtime tests.

Thank you,
George