docker: split minimum setup to separate script

setup

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+# Minimum requirements to run ./build --download-dependencies
+y=
+if [ $# -eq 1 ]; then
+  y=-y
+fi
+apt-get update
+apt-get install $y \
+  git \
+  python3 \
+  python3-distutils \
+;