ipaldap: merge simple_bind into LDAPClient
* Use LDAPClient.simple_bind instead of extra call to IPAdmin.do_simple_bind
* Rename binddn to bind_dn
* Rename bindpw to bind_password
* Explicitly specify bind_dn in all calls
https://fedorahosted.org/freeipa/ticket/6461
Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Jan Cholasta <jcholast@redhat.com>