During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
This should mean that logs from worker processes are flushed before shutdown.
When a test completes, Complement stops the docker container, which means that
synapse will receive a SIGTERM. Currently, the `complement_fork_starter` exits
immediately (without notifying the worker processes), which means that the
workers never get a chance to flush their logs before the whole container is
vaped. We can fix this by propagating the SIGTERM to the children.
