If we're activating the device without knowing the connection in advance, defer
servicing the requests for the secrets until we set the path.

[lkundrak@fedora20-2 ~]$ nmcli --ask c ifname wlan0

(process:18405): libnm-CRITICAL **: nm_object_get_path: assertion 'NM_IS_OBJECT (object)' failed
Error: Connection activation failed: The device has no connections available.
[lkundrak@fedora20-2 ~]$