RFR(XS): 8132374: AIX: fix value of os.version property

[Volker Simonis]

Hi,

can somebody please review this tiny fix to get the value of the
'os.version' property correct on AIX:

http://cr.openjdk.java.net/~simonis/webrevs/2015/8132374/
https://bugs.openjdk.java.net/browse/JDK-8132374

Thank you and best regards,
Volker