s4:torture/samba3rpc: let rpc.authcontext be more robust against low level changes...

s4:torture/samba3rpc: let rpc.authcontext be more robust against low level changes (part2)

We now use smbXcli_conn_is_connected() and
dcerpc_binding_handle_is_connected() to verify only the dcerpc layer
got an error. The expected error is EIO mapped to NT_STATUS_IO_DEVICE_ERROR.

NT_STATUS_INVALID_HANDLE should only be visible at the SMB layer,
but we keep this as allowed return value for now, until
the dcerpc layer is fixed.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>