Latest version of Pipeline hangs on each job

[bertfrees]

Happens only when installed on SBS test server, not on my development machine. I'm not sure whether the problem exists on the SBS server that is used to run dtbook-to-odt. This is another case where it would help if we'd run inside Docker.

[bertfrees]

We are using Docker now. The Pipeline seems to work fine when run inside the container, but it needs to be further tested. The images will be available at https://hub.docker.com/r/sbsdev/pipeline2 and automatically updated after each commit.