Add debug occ command to check that the LDAP group membership is correctly configured

[sorbaugh]

Currently, when looking an LDAP user, the membersOf attribute correctly lists the groups the user is a member of. When looking at an LDAP group, the responsible attribute does not always show a correct list of members. This is a common error due to an LDAP misconfiguration. With this command, we'd be able to quickly spot this.