Disable WiFi autojoin when user decides via "Stay connected?" dialog

If the user selects "No" in the "Stay connected?" dialog box:
1. Disable autojoining that network in the future, and
2. Disassociate from that network.

Bug:22187193
Change-Id: I14dc9236c57e3ab7d3ec95edc906787cbfbf3c9f