Allow non-persistent manual network selection.

Allow the API to specify if the selection should be persisted across reboots.
This also has the side affect of not notifying the user when signal is lost.

Necessary becasue the API might be used transparent to the user and the
notifications will be bizarre.

Bug: 23971948
Change-Id: Ibb15144fb8a61f63a9c967d875d9ce8c70520ff0