stage1/usr_from_coreos: add new image signing subkey 0638EB2F
stage1/usr_from_coreos: add new image signing subkey 0638EB2F

joshix/rkt,joshix/rkt,coreos/rkt,rkt/rkt,joshix/rkt,kinvolk/rkt,kinvolk/rkt,kinvolk/rkt,lucasallan/rkt,lucasallan/rkt,rkt/rkt,lucasallan/rkt,rkt/rkt,kinvolk/rkt,lucasallan/rkt,joshix/rkt,coreos/rkt,rkt/rkt,coreos/rkt