fix(opm-index-add) Throw error when a bundle is invalid

With the introduction of operator-framework#503, when a bundle from the list of bundles
being added with the `opm index add` command was invalid, opm was not
throwing an error, and was building the index with the valid bundles
instead, even when the `permissive` mode was not enabled. This PR
fixes the issue.

pkg/registry/input_stream.go

@@ -142,7 +142,7 @@ func (r *ReplacesInputStream) Next() (*ImageInput, error) {
 				delete(r.packages, pkg)
 			}
 
-			return image, nil
+			return image, utilerrors.NewAggregate(errs)
 		}
 
 		// No viable bundle found in the package, can't parse it any further