RFR: JDK-8232092 (fs) Files::isWritable returns false on a writeable root directory (win) [v9]

[Alan Bateman]

Nhat,

The test is failing intermittently, tracked as JDK-8254195. I didn't see 
this when testing your change before sponsoring.

I think the issue is that there are several tests running at the same 
time so the unallocated and unusable values won't be stable. I think we 
can drop those from the test.

-Alan

[1] https://bugs.openjdk.java.net/browse/JDK-8254195