auto forward DOCKER_HOST env var

drun

@@ -117,12 +117,14 @@ if [ -f '/proc/1/cgroup' ]; then
 fi
 
 DSOCK=/var/run/docker.sock
-if [ "${MOUNTDOCKERSOCK:-}" != 'n' -a -r "$DSOCK" -a  -w "$DSOCK" -a -S "$DSOCK" ]; then
+if [ "${MOUNTDOCKERSOCK:-}" != 'n' -a -r "$DSOCK" -a -w "$DSOCK" -a -S "$DSOCK" ]; then
   if curl --help | grep -q unix-socket && curl -sS --unix-socket "$DSOCK" http://docker/_ping | grep -q OK; then
     EXTRA_OPTS="${EXTRA_OPTS:-} -v ${DSOCK}:${DSOCK}"
   elif nc -h 2>&1 | grep -qe '-X\b' && printf 'GET /_ping HTTP/1.1\nHost: daemon\n\n' | nc -U "$DSOCK" | head -n 1 | grep -q '200 OK'; then
     EXTRA_OPTS="${EXTRA_OPTS:-} -v ${DSOCK}:${DSOCK}"
   fi
+elif [ -n "${DOCKER_HOST}" ]; then
+  EXTRA_OPTS="${EXTRA_OPTS:-} -e DOCKER_HOST=${DOCKER_HOST}"
 fi
 
 RM_OPT=${RM_OPT=--rm}