Only finish Setup Wizard Activity when fully done

Wait for the ACTION_FINISHED broadcast before finishing the Activity.
This prevents the Setup Wizard from being re-launched when it is still
set as the default home screen, which it continues to be until the
exit worker changes as part of its finishSetupWizard call.

Skip SetupWizardExitActivity during the normal finish process, moving
common exit operations to SetupWizardUtils.

Change-Id: I1c59553e7dcaf934fb81dce9bf901ec0f2bb7b59