Fix LDAPCreate search failure
LDAPCreate reports "search criteria was not specific enough" when LDAP
object created in LDAPCreate shares its container with other LDAP objects
and there is one with the same name and RDN attribute.
Pass objectclass to find_entry_by_attr() function used to retrieve
newly created object for POST_CALLBACK to identify correct LDAP
object.
https://fedorahosted.org/freeipa/ticket/1864