Merge upstream changes from Marlin 2.1.2.1

docker/Dockerfile

@@ -1,7 +1,24 @@
 FROM python:3.9.0-buster
 
-RUN pip install -U platformio
+# Disable warnings about not having a TTY
+ARG DEBIAN_FRONTEND=noninteractive
+
+# Disable debconf warnings
+ARG DEBCONF_NOWARNINGS="yes"
+
+# Upgrade pip
+RUN pip install --upgrade pip
+
+# Install platformio toolchain / framework and pyyaml
+RUN pip install -U platformio PyYaml
+
+# Upgrade platformio using development version / branch
 RUN pio upgrade --dev
-# To get the test platforms
-RUN pip install PyYaml
+
+# Set working directory
+WORKDIR /code
+
+# Set volumes / mount points that we are using
+VOLUME /code /root/.platformio
+
 #ENV PATH /code/buildroot/bin/:/code/buildroot/tests/:${PATH}