Launch existing Task when taskId is given to ConfirmDeviceCredential

When using ConfirmDeviceCredential as the Work Challenge, we sometimes
have intercepted a task launching from recents. In this case, read the
taskId given as an extra and request that task to be started from
recents instead of launching a new intent.

Change-Id: Icca92f246e8f025b64de1f138493fc4069f98829