New explicit Docker selection based on environment variable

Everything else breaks after a few years I give up.

Dockerfile

@@ -2,5 +2,7 @@
 FROM ubuntu:20.04
 COPY setup /
 COPY requirements.txt /
+# https://stackoverflow.com/questions/23513045/how-to-check-if-a-process-is-running-inside-docker-container/65942222#65942222
+ENV LKMC_IN_DOCKER=true
 RUN /setup -y
 CMD bash