linter: enable nilerr

A number of cases looked suspicious, so I marked them with `FIXME`s to
leave some breadcrumbs.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

pkg/util/utils.go

@@ -727,7 +727,7 @@ func SocketPath() (string, error) {
 func LookupUser(name string) (*user.User, error) {
 	// Assume UID look up first, if it fails lookup by username
 	if u, err := user.LookupId(name); err == nil {
-		return u, err
+		return u, nil
 	}
 	return user.Lookup(name)
 }