objects: Fix InstanceGroup.obj_make_compatible()

The obj_make_compatible() method of the InstanceGroup object
incorrectly assumed the format of the version argument was the version
broken down into int() parts.  It comes in as a string and must be
converted.

Change-Id: Id2724c5029202f001e5a2b4371f030b65c72fdfd
Merge "objects: Fix InstanceGroup.obj_make_compatible()"