(CFACT-64) Add structured operating system fact

This commit adds a new 'os' structured fact, which returns a map
including keys for each of the operatingsystem-releated facts. The
fact also includes LSB keys in Linux systems where LSB is available.
(maint) Resolve operatingsystemmajrelease in Ubuntu

This commit adds Ubuntu to the map of platforms which
are suitable to resolve the operatingsystemmajrelease fact,
and adds the necessary logic to do so.