Ldap tests should wait for connection reaper to be terminated

Need to find the way to guarantee that the thread pool where Ldap connection reaper is running is terminated before the test end.

LDAPManagerImpl owns LDAPRunnerImpl, which owns LDAPConnectionFactory, which owns LDAPConnectionReaper. However the connection implementations (e.g. OpenLDAPConnection) also own a shared pointer to the LDAPConnectionReaper, which means deleting the LDAPConnectionFactory doesn't force the reaper to terminate.