Hide notification shade when WifiDebuggingActivity is shown.

Wireless debugging can be enabled from a quick settings tile, and this
gets covered by the notification shade.

Bug: 153275926

Test: Enable wifi debugging qstile from Settings > Developer options >
Quick settings developer tiles > Wireless debugging. On notification
shade, enable wireless debugging on an untrusted network. Notification
shade should be hidden to reveal the WifiDebuggingActivity.

Change-Id: I347e23ab85ee1235c20eab9a2318e1d8afe8975a