Fix docker.sh by specifying entrypoint

Newer flowdalic/gentoo-dev images have ENTRYPIONT specified, this
prevents arguments from being passed to the docker run entrypoint,
which is tools/docker-prepare in case of docker.sh.

To fix that, we invoke "docker run" with "--entrypoint
tools/docker-preapre" in docker.sh.

docker.sh

@@ -12,5 +12,6 @@ docker run \
 	   --env USER_ID="${UID}" \
 	   --env GROUP_ID="$(id -g ${USER})" \
 	   --security-opt=seccomp:unconfined \
+	   --entrypoint "${EMPER_ROOT}/tools/docker-prepare" \
 	   "${IMAGE}" \
-	   "${EMPER_ROOT}/tools/docker-prepare" "${EMPER_ROOT}" $@
+	   "${EMPER_ROOT}" "$@"