Use startActivityAsUser instead of startActivity
in WifiOnboarding.

Bug: 282210693
Test: atest WakeupOnboardingTest
Test: Manual Test
       1. Disable the shouldShowNotification check
          in WakeupOnboarding#maybeShowNotification.
       2. Start as the main user.
       3. Disable Wifi. This will bring up the
          wakeup notification.
       4. Click the notification. Ensure that the
          Network Preferences menu is opened.
       5. Switch to a secondary user.
       6. Repeat steps 3 and 4.
Change-Id: I0a869799d9a5a4a57fcade9b253b7f6327367205
2 files changed