Support for docker images that set the USER directive. Changes the

docker user to root for the init script to configure the network,
then drops to the configured user (or root if one is not defined)
for continuing booting the image.

gns3server/compute/docker/resources/init.sh

@@ -87,6 +87,9 @@ done
 ifup -a -f
 
 # continue normal docker startup
-PATH="$OLD_PATH"
-exec "$@"
-
+GNS3_CMD="PATH=$OLD_PATH exec"
+while test "$#" -gt 0 ; do
+    GNS3_CMD="${GNS3_CMD} \"${1//\"/\\\"}\""
+    shift
+done
+exec su ${GNS3_USER-root} -p -c "$GNS3_CMD"