gPlazma ldap: hardcoded RDN OID

[paulmillar]

The LDAP gPlazma plugin contains the following code:

peopleOU = String.format("ou=%s,%s", peopleTree, organization);
groupOU = String.format("ou=%s,%s", groupTree, organization);

Note how the ou= is hard-coded when building these two DN.

This is bad because not all institutes identify people and groups via an ou-based RDN.

The LDAP configuration should be adjusted to allow more flexibility in building the DN under which people and groups are searched.