Various Docker image upgrades, read the entire commit message!

- Ubuntu 17.10 → 18.04.
- Python 3.6.3 → 3.6.6.
- Use `DEBIAN_FRONTEND=noninteractive` to prevent prompts during
  installation.
- Install `tzdata` in the base image as it's required by subimages.
- Correctly set maintainer in Dockerfile.

docker/2_buildpy/buildpy.docker

@@ -1,9 +1,9 @@
 FROM pillar_base
-LABEL maintainer Sybren A. Stüvel <sybren@blender.studio>
+LABEL maintainer="Sybren A. Stüvel <sybren@blender.studio>"
 
 RUN sed -i 's/^# deb-src/deb-src/' /etc/apt/sources.list && \
     apt-get update && \
-    apt-get install -qy \
+    DEBIAN_FRONTEND=noninteractive apt-get install -qy \
         build-essential \
         apache2-dev \
         checkinstall \
@@ -11,13 +11,13 @@ RUN sed -i 's/^# deb-src/deb-src/' /etc/apt/sources.list && \
 
 RUN apt-get build-dep -y python3.6
 
-ADD Python-3.6.4.tar.xz.md5 /Python-3.6.4.tar.xz.md5
+ADD Python-3.6.6.tar.xz.md5 /Python-3.6.6.tar.xz.md5
 
 # Install Python sources
-RUN curl -O https://www.python.org/ftp/python/3.6.4/Python-3.6.4.tar.xz && \
-    md5sum -c Python-3.6.4.tar.xz.md5 && \
-    tar xf Python-3.6.4.tar.xz && \
-    rm -v Python-3.6.4.tar.xz
+RUN curl -O https://www.python.org/ftp/python/3.6.6/Python-3.6.6.tar.xz && \
+    md5sum -c Python-3.6.6.tar.xz.md5 && \
+    tar xf Python-3.6.6.tar.xz && \
+    rm -v Python-3.6.6.tar.xz
 
 # Install mod-wsgi sources
 RUN mkdir -p /dpkg && cd /dpkg && apt-get source libapache2-mod-wsgi-py3
@@ -32,4 +32,4 @@ RUN echo /opt/python/lib > /etc/ld.so.conf.d/python.conf
 RUN ldconfig
 ENV PATH=/opt/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
 
-ENV PYTHONSOURCE=/Python-3.6.4
+ENV PYTHONSOURCE=/Python-3.6.6