RFR: 8255787: Tag container tests that use cGroups with cgroups keyword

[Harold Seigel]

Please review this small change to add a cgroups keyword to tests that use cgroups.  The fix was tested by running Mach5 container tests.

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Commit messages:
 - 8255787: Tag container tests that use cGroups with cgroups keyword

Changes: https://git.openjdk.java.net/jdk/pull/1148/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1148&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255787
  Stats: 20 lines in 15 files changed: 15 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1148.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1148/head:pull/1148

PR: https://git.openjdk.java.net/jdk/pull/1148