Move the shared pipework script to the base image, and call it in
ttcn3-docker-run.sh if WAIT_FOR_NETDEV is set. Use ttcn3-docker-run.sh
as entrypoint in both Dockerfiles and remove the custom entrypoint
scripts (which are the same as ttcn3-docker-run.sh now).
Related: OS#5017
Change-Id: I2889abe94ed522a205890e5cb39e09cbebfbd820
