One can pass --stream to zdtm.py for testing criu with image streaming.
criu-image-streamer should be installed in ../criu-image-streamer
relative to the criu project directory. But any path will do providing
that criu-image-streamer can be found in the PATH env.
Added a few tests to run on travis-ci to make sure streaming works.
We run test that are likely to fail. However, it would be good to once
in a while run all tests with `--stream -a`.
Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
