[11u] RFR 8265231: (fc) ReadDirect and WriteDirect tests fail after fix for JDK-8264821

[Zhengyu Gu]

I would like to backport this patch to 11u for parity with Oracle 11.0.13.

The original bug: https://bugs.openjdk.java.net/browse/JDK-8265231
The original patch: https://github.com/openjdk/jdk/commit/d1b28e7a

The original patch does not apply cleanly, due to JDK-8262465 11u 
backport diverged from original patch, and preserved 
isDirectIOSupportedByFS check.

11u webrev: http://cr.openjdk.java.net/~zgu/JDK-8265231-11u/webrev.00/


Test:
   DirectIOTest.java passed on Linux x86_64

Thanks,

-Zhengyu