(FACT-692) Fix issue with Solaris resolution of operatingsystemmajrelease

This commit corrects the naming of the method responsible for
determining the major release of SunOS systems, allowing Solaris 10
systems to correctly resolve the operatingsystemmajrelease fact.

This issue didn't manifest itself in Solaris 11 systems because the base
major release implementation correctly determined the Solaris 11 major release.
Is this because of some meta-programming `method_missing` action?