Update docker scripts

Update docker scripts

- docker-build: Allow DOCKER_ARGS to be empty. This is not
a required parameter, it can be empty.
- docker-get-git-describe: Remove container reference. The
CONTAINER_PUSH_REGISTRY already gets added in the docker-push
script. No need to add it again. Only process the tag variable.
- docker-get-yaml-tag: Rename image_name to image_build_tag
to match docker-get-git-describe. Add missing "DOCKER_NAME" in
the DOCKER_IMAGE. Only process the tag variable.
- docker-push: Update the correct image name and tag in the push
command.

Change-Id: Ic3aad7ae0f87b589ce5d57f6848f7e8e75f9b71e
Signed-off-by: Jessica Wagantall <jwagantall@linuxfoundation.org>