8181919: Refactor test/java/io/File/GetXSpace.sh to java test

[Brian Burkhalter]

To fix [1], please consider the patch [2]. This follows on from the proposed change [3] which in turn follows from [4].

Thanks,

Brian

[1] https://bugs.openjdk.java.net/browse/JDK-8181919
[2] http://cr.openjdk.java.net/~bpb/8181919/webrev.00/
[3] https://mail.openjdk.java.net/pipermail/core-libs-dev/2020-August/068025.html (GetXSpace should not run on AIX)
[4] http://mail.openjdk.java.net/pipermail/core-libs-dev/2020-July/067990.html (GetXSpace fails on macOS)