I just tried to rebuild my Docker image, but the process gets interrupted during provision_js.sh; it seems gyp requires a binary "python", which usually is just a symlink to the installed version. This is not created. I solved by adding a line to the dockerfile "RUN apt-get install -y python2.7 && ln -s /usr/bin/python27 /usr/bin/python".
Now, it builds, but that seems very hacky to me and I do not understand why docker build is complaining now. Maybe it is the change of the base image?