RFR 9 8161039 : System.getProperty("os.version") returns incorrect version number on Mac

[Brent Christian]

Hi,

The fix for 7131356 introduced a minor behavior change in the value of 
the "os.version" system property on MacOS.

On systems running an OS with a patch version of 0, we've started 
including this in the value of os.version (e.g. "10.11.0"), whereas 
before the trailing ".0" was omitted.

Please review this fix, which restores the previous behavior.

Bug: https://bugs.openjdk.java.net/browse/JDK-8161039
Webrev: http://cr.openjdk.java.net/~bchristi/8161039/webrev.00/

Thanks!
-Brent