RFR: 8298619: java/io/File/GetXSpace.java is failing

[Brian Burkhalter]

Modify the `Space` instances used for size comparison to be created with total number of bytes derived from the Windows `diskFree` utility instead of Cygwin’s `df`.

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Commit messages:
 - 8298619: java/io/File/GetXSpace.java is failing

Changes: https://git.openjdk.org/jdk/pull/12397/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12397&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298619
  Stats: 53 lines in 1 file changed: 37 ins; 1 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/12397.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12397/head:pull/12397

PR: https://git.openjdk.org/jdk/pull/12397