Use LDIF config and add mdb support in t_kdb.py

Use LDIF config and add mdb support in t_kdb.py

When setting up slapd, use slapadd with cn=config LDIF directives
instead of the deprecated config file.  By adding one cn=config object
at a time, we can detect specific specific configuration failures,
including unsupported database types.  Try the mdb and bdb database
types, to work with older and newer OpenLDAP versions.