Fix issue #81 (Coverage raises warnings when running in multiprocessing).

12 jobs for master in 18 minutes and 49 seconds (queued for 1 second)
Name Stage Failure
failed
pages Deploy
$ mkdir -p public/img
$ mkdir -p public/coverage
$ mkdir -p public/test_reports
$ cp -r docs/_build/html/* public/doc/
$ cp -r docs/img/* public/img/
$ cp -r htmlcov/* public/coverage/
cp: cannot stat 'htmlcov/*': No such file or directory
Cleaning up file based variables
ERROR: Job failed: exit code 1