scope: use same Docker args for early dry run

`launch` first does a `scope --dry-run` to parse and validate Scope
cmdline arguments before starting the main Scope container and
processes. Use the same Docker args for the dry run to make sure the
container has the same privileges and mount points. Otherwise valid
`$WEAVESCOPE_DOCKER_ARGS` might fail here.

scope

@@ -165,14 +165,20 @@ create_plugins_dir() {
         "$SCOPE_IMAGE" -c "mkdir -p /var/run/scope/plugins"
 }
 
-launch_command() {
+docker_args() {
     # shellcheck disable=SC2086
-    echo docker run --privileged $USERNS_HOST -d --name="$SCOPE_CONTAINER_NAME" --net=host --pid=host \
+    echo --privileged $USERNS_HOST --net=host --pid=host \
         -v /var/run/docker.sock:/var/run/docker.sock \
         -v /var/run/scope/plugins:/var/run/scope/plugins \
         -v /sys/kernel/debug:/sys/kernel/debug \
         -e CHECKPOINT_DISABLE \
-        $WEAVESCOPE_DOCKER_ARGS "$SCOPE_IMAGE" --probe.docker=true
+        $WEAVESCOPE_DOCKER_ARGS
+}
+
+launch_command() {
+    # shellcheck disable=SC2046
+    echo docker run -d --name="$SCOPE_CONTAINER_NAME" $(docker_args) \
+        "$SCOPE_IMAGE" --probe.docker=true
 }
 
 launch_docker4mac_app_command() {
@@ -228,8 +234,8 @@ case "$COMMAND" in
     launch)
         # Do a dry run of scope in the foreground, so it can parse args etc
         # avoiding the entrypoint script in the process.
-        # shellcheck disable=SC2086
-        docker run --rm -e CHECKPOINT_DISABLE --entrypoint=/home/weave/scope $WEAVESCOPE_DOCKER_ARGS "$SCOPE_IMAGE" --dry-run "$@"
+        # shellcheck disable=SC2046
+        docker run --rm --entrypoint=/home/weave/scope $(docker_args) "$SCOPE_IMAGE" --dry-run "$@"
 
         if check_docker_for_mac; then
             create_plugins_dir