QPID-6132: [Java Broker] Mark SimpleLDAP attributes providerUrl, searchFilter, searchContext as mandatory.

Also:

* 'ping' the Directory on object creation/change (rationale: discover config errors early, rather than awaiting the first auth)
* Reinstate the LDAP context factory class default.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1629664 13f79535-47bb-0310-9956-ffa450edef68
QPID-6126: [Java Broker] Improve error message when object goes into the errored state.  Add a couple of missing licences

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1629666 13f79535-47bb-0310-9956-ffa450edef68