(FACT-651) added KVM detection for SunOS

On one of my few KVM-virtualized Solaris instances, I noticed the detection of being virtual or not wasn't working properly. Note: I'm running OpenIndiana, and possibly on Solaris itself the path to prtconf could be different.

@skoef one change we can make here is to just check if `Facter.value(:kernel) == "SunOS"` rather than iterating over a single element array.