core: Fix broken backward compatibility of os ids

This fix is about maintaining oss backward compatibility mappings of
old os names to the current IDs.

Vm Import/Export is using the os unique name instead of the os ID in the
OVF and since all unique names streamlined with the REST API
representation they all are not identified and fallback ID 0 - "other"

pre-osinfo exports would write the OS Windows8 while the new name is
windows_8 and so on

Solution:

Added a backward compatibility section to osinfo-default.properties

    # Since Unassigned is removed we translate is to other so
    backwardCompatibility.Unasigned = 0
    backwardCompatibility.Other = 0

    # represents the current id of old Windows8 os
    backwardCompatibilty.Windows8 = 20

Bug-Url: https://bugzilla.redhat.com/1006340
Change-Id: I77c51a3bd0f4f0c264e8f895f40fd4d2bf4d689c
Signed-off-by: Roy Golan <rgolan@redhat.com>