core: osinfo - Fix Unassigned conversion to UNASSIGNED

Fixed the pattern matching to cover all the rest OsType names
Added test cases to cover all the OsType names.

This fixed the backward compatibility UNASSIGNED OsType value.

Change-Id: Ib55fd00ddfb19aff8bf38d1ca0da923146956ccd
Signed-off-by: Roy Golan <rgolan@redhat.com>