Install the update-payload-key in the recovery image as well.

The update-payload-key is required to verify the contents of the OTA in
recovery while sideloading an update.

Bug: 27178350
TEST=`make` builds a boot.img with the payload key in recovery.

(cherry picked from commit c6ebe9fc)

Change-Id: I0128d7f684d32201e227acce798b25f12982eaaa