Fixes #13980.

--- fsmo.py.old	2019-05-30 13:01:03.174095515 -0400
+++ fsmo.py.new	2019-05-29 15:46:45.552101604 -0400
@@ -18,6 +18,7 @@
 #
 
 import samba
+import samba.drs_utils
 import samba.getopt as options
 import ldb
 from ldb import LdbError