add IsNotMountPoint() to mount_unsupported.go

Signed-off-by: Huamin Chen <hchen@redhat.com>

pkg/util/mount/mount_unsupported.go

@@ -57,3 +57,7 @@ func (mounter *SafeFormatAndMount) formatAndMount(source string, target string,
 func (mounter *SafeFormatAndMount) diskLooksUnformatted(disk string) (bool, error) {
 	return true, nil
 }
+
+func IsNotMountPoint(file string) (bool, error) {
+	return true, nil
+}