John Rowley authored Mar 15, 2018 and Pål Karlsrud committed Jun 19, 2018

The MUTABLE_IMAGE_RUDDER variables was using the DOCKER_VERSION instead of MUTABLE_VERSION
```
MUTABLE_IMAGE        := ${DOCKER_REGISTRY}/${IMAGE_PREFIX}/${SHORT_NAME}:${MUTABLE_VERSION}
MUTABLE_IMAGE_RUDDER := ${DOCKER_REGISTRY}/${IMAGE_PREFIX}/${SHORT_NAME_RUDDER}:${DOCKER_VERSION}
```