Start the LDAPReaper threadpool

The LDAPReaper uses a foreign threadpool to offload LDAP disconnect operations. However startup is never called on the underlying threadpool, which means worker threads are not spawned or actively processing disconnections. This may result in an increasing number of active connections.

To help mitigate the impact on file descriptor usage of this connection leak, enable LDAP connection pooling to greatly reduce the number of connections opened/closed.