Patch merged into coreboot/master: util/docker: Update makefile with command to kill docker images

the following patch was just integrated into master:
commit af25fd78e8edcf0d46acdd5f45d1379770753b30
Author: Martin Roth 
Date:   Fri Dec 30 16:12:30 2016 -0700

util/docker: Update makefile with command to kill docker images

Kill running docker containers before trying to remove images or
    containers.

Change-Id: Id2de90edbe5d0dc6ecb906be7101ad9744dbd11e
    Signed-off-by: Martin Roth 
    Reviewed-on: https://review.coreboot.org/17999
    Tested-by: build bot (Jenkins)
    Reviewed-by: Paul Menzel 
    Reviewed-by: Patrick Georgi

See https://review.coreboot.org/17999 for details.

-gerrit