WIP breaking stuff: updating docker image build process for Python 3.6

This requires a new way to pass requirements.txt files to Docker (since
they now link to each other), as well as building Python ourselves (since
even Ubuntu 16.10 doesn't have a decent Python 3.6).

This is just a WIP commit, will be fixed soon(ish).

docker/2_build/myconfigure

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+./configure \
+    --prefix=$PYTHONTARGET \
+    --enable-ipv6 \
+    --enable-optimizations \
+    --enable-shared \
+    --with-ensurepip=upgrade