RFR: 8283279: [Testbug] Improve TestGetSwapSpaceSize

[Severin Gehwolf]

Please review this container test improvement. The test in question only makes sense iff the total swap space size as reported by the container aware OperatingSystemMXBean is `0`. If that's not the case, then something else might be amiss, e.g. OperatingSystemMXBean reporting the host swap limits. In such a case a passing test tells us nothing. Certainly not if the
fix from [JDK-8242480](https://bugs.openjdk.java.net/browse/JDK-8242480) is present or not.

Testing:
- [x] Manual with and without the code fix of JDK-8242480. Still passes with the fix, and fails without. Tested the test on cgroups v1 and cgroups v2.

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Commit messages:
 - 8283279: [Testbug] Improve TestGetSwapSpaceSize

Changes: https://git.openjdk.java.net/jdk/pull/7854/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7854&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283279
  Stats: 29 lines in 2 files changed: 22 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7854.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7854/head:pull/7854

PR: https://git.openjdk.java.net/jdk/pull/7854