RFR: 8274750: java/io/File/GetXSpace.java failed: '/dev': 191488 != 190976

[Brian Burkhalter]

Please consider this proposed change to ignore comparing the total size of `/dev` as returned by `DF(1)` and `STAT(2)` on macOS.

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Commit messages:
 - 8274750: java/io/File/GetXSpace.java failed: '/dev': 191488 != 190976

Changes: https://git.openjdk.java.net/jdk/pull/6122/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6122&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274750
  Stats: 8 lines in 1 file changed: 7 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6122.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6122/head:pull/6122

PR: https://git.openjdk.java.net/jdk/pull/6122