RFR(XS): 8227317: [TESTBUG] jdk docker/TestDockerMemoryMetrics.java fails on systems w/o kernel memory accounting

[mikhailo.seledtsov at oracle.com]

Please review this change that adds extra check for test case 
testKernelMemoryLimit(). If system does not support kernel memory 
accounting then verification for this test case is skipped.

     JBS: https://bugs.openjdk.java.net/browse/JDK-8227317
     Webrev: http://cr.openjdk.java.net/~mseledtsov/8227317.01/
     Testing:
        1. Ran the test on systems with disabled kernel memory 
accounting before and after the fix - fix works
        2. Ran the test case 60 times on multiple Linux-x64 systems - no 
failures


Thank you,
Misha