RFR: 8206456 - [TESTBUG] docker jtreg tests fail on systems without cpuset.effective_cpus / cpuset.effective_mem

[Bob Vandette]

Please review this fix which eliminates some docker/cgroup test failures when running on older
Linux kernels with missing cgroup metric files.

BUGS:
https://bugs.openjdk.java.net/browse/JDK-8206456

WEBREV:
http://cr.openjdk.java.net/~bobv/8206456/webrev/

This fix has been verified by the reporter of the issue.

Bob.