RFR (S) 8154566: os_linux.cpp parse_os_info gives non descriptive output on current SLES releases

[Coleen Phillimore]

Summary: For SuSE, read the first line of the /etc/xrelease file, also 
get PRETTY_NAME from /etc/os_release
Contributed-by: matthias.baesken at sap.com, coleen.phillimore at oracle.com

See discussion: 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2016-April/022720.html

open webrev at http://cr.openjdk.java.net/~coleenp/8154566.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8154566

Tested by Matthias on SuSE and myself on OEL 6.0 and Ubuntu.  Ran 
hotspot/test/runtime jtreg tests.

Thanks,
Coleen