[test] Pull docker images once before begin of tests (during buildout or conda-build)

2 jobs for issue-63 in 2 minutes and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
canceled #157625
docker-build
build_linux_36

00:02:44

canceled #157626
macosx
build_macosx_36

00:02:47