Allow WiFi picker to exit after a valid connection is made

Choice is passed in via boolean extra and has two effects:
* A valid network connection exits the picker.
* The next button (if there is one) is hidden.

This functionality will be used for SetupWizard initially.

Bug: 6428046
Change-Id: Ieeed3a9f1013cccd76bd4762131747a57a38ce9c