WIP: more work on the docker structure, still not finished with 4_run

1_base: builds a base image, based on Ubuntu 16.10
2_buildpy: builds two images:
	2a: an image that can build Python 3.6
	2b: an image that contains the built Python 3.6 in /opt/python
3_buildwheels: builds an image to build wheel files, puts them in ../4_run
4_run: the production runtime image, which can't build anything and just runs.

docker/2_buildpy/build.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+
+set -e
+
+# macOS does not support readlink -f, so we use greadlink instead
+if [ $(uname) == 'Darwin' ]; then
+    command -v greadlink 2>/dev/null 2>&1 || { echo >&2 "Install greadlink using brew."; exit 1; }
+    readlink='greadlink'
+else
+    readlink='readlink'
+fi
+
+PYTHONTARGET=$($readlink -f ./python)
+
+mkdir -p "$PYTHONTARGET"
+echo "Python will be built to $PYTHONTARGET"
+
+docker build -t pillar_build -f buildpy.docker .
+
+# Use the docker image to build Python 3.6.
+GID=$(id --group)
+docker run --rm -i \
+    -v "$PYTHONTARGET:/opt/python" \
+    pillar_build <<EOT
+set -e
+cd \$PYTHONSOURCE
+./configure \
+    --prefix=/opt/python \
+    --enable-ipv6 \
+    --enable-shared \
+    --with-ensurepip=upgrade
+make -j8 install
+chown -R $UID:$GID /opt/python/*
+EOT
+
+# Create another docker image which contains the actual Python.
+# This one will serve as base for the Wheel builder and the
+# production image.
+docker build -t pillar_py:3.6 -f includepy.docker .