tests/rodc_rwdc: p.communicate() gives bytes, not str

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

source4/dsdb/tests/python/rodc_rwdc.py

@@ -88,7 +88,7 @@ def set_auto_replication(dc, allow):
                              stdout=subprocess.PIPE)
         stdout, stderr = p.communicate()
         if p.returncode:
-            if 'LDAP_REFERRAL' not in stderr:
+            if b'LDAP_REFERRAL' not in stderr:
                 raise RodcRwdcTestException()
             print("ignoring +%s REFERRAL error; assuming %s is RODC" %
                   (opt, dc))