_find_group: made OID-match logic more correct ISSUE=6218
_find_group: made OID-match logic more correct ISSUE=6218

I also did a little rearrangement of the last part of the method in preparation
for the next bit of work.

GlobalNOC/simp,GlobalNOC/simp,GlobalNOC/simp,GlobalNOC/simp,GlobalNOC/simp