Use --load with "docker build"

If --load is not provided to "docker build" command, the image only
remains in the local cache and is not available for use locally when
doing "docker run rustvmm/dev:$VERSION" like the README suggests.

Without this change using the image locally is not possible, the image
does not show up when doing `docker image ls` and the tag is not found
when doing `docker run <TAG>`. the `docker build` step prints this
warning: "WARNING: No output specified with docker-container driver.
Build result will only remain in the build cache."

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>

Author: epilys

docker.sh

@@ -48,6 +48,7 @@ build_tag(){
 build(){
   new_tag=$(build_tag)
   docker build -t "$new_tag" \
+        --load \
         --build-arg GIT_BRANCH="${GIT_BRANCH}" \
         --build-arg GIT_COMMIT="${GIT_COMMIT}" \
         -f Dockerfile .