Prevent 'DSID-0C0906E8' error when binding to ActiveDirectory.

When binding (using `binddn` and `bindpw`) to an ActiveDirectory for LDAP lookups without explicitely setting `anonymous=False`, the LDAP search will fail with `DSID-0C0906E8`.

This fixes the issue for me and I can finally use LDAP pillars without looking at backtraces in my master log :)