Merge pull request moby#3529 from tonistiigi/fix-shell

hack: add correct entrypoint to shell script

Author: tonistiigi

hack/shell

@@ -21,4 +21,4 @@ if [ -n "$MOUNT_BUILDKIT_SOURCE" ]; then
 fi
 
 set -x
-docker run $SSH $volumes -it --privileged -v /tmp --net=host -e BUILDKIT_REGISTRY_MIRROR_DIR=/root/.cache/registry --rm $(cat $iidfile)
+docker run $SSH $volumes -it --privileged -v /tmp --net=host --entrypoint ash -e BUILDKIT_REGISTRY_MIRROR_DIR=/root/.cache/registry --rm $(cat $iidfile)