Changes

ttcn3-fr-test/jenkins.sh: revert docker run --rm

Revert the change of adding a --rm to the "docker run" commands done in
I48b01c43fedf379b8a565eaab0369806d7831bd8.

This script runs the containers in the background, waits until they are
done, copies the logs and then removes them afterwards.

Fix for:
  + docker kill jenkins-ttcn3-fr-test-384-frnet
  jenkins-ttcn3-fr-test-384-frnet
  + docker logs --timestamps jenkins-ttcn3-fr-test-384-ttcn3-fr-test
  Error: No such container: jenkins-ttcn3-fr-test-384-ttcn3-fr-test

Change-Id: I56dc07820ccfa8ad6936764262a7c6c272e59c37

ttcn3-fr-test/jenkins.sh: make use of clean_up()

Move cleaning up logic to clean_up(), so it runs as part of the
clean_up_trap if any command in the previous code fails.

For example, if the first docker container started properly, but the
second docker container failed to start: without this patch, it would
just stop the script without running the clean up code.

Change-Id: I4624e37d5d2fa90b71b32d72067b3645f69805da