'seems to fix random tests crashes (the main change is "cli.stop()" line remove)

I'm not sure about that but it seems that closing the ZMQ socket here is not a good idea because the main loop is the same between tests.
no more random tests crashes
fix some random failing tests on linux (I don't undestand why but it worked on osx ?)
update (no more random crashes ?)
flake8 fixes
do not execute circusweb tests because of #580
Merge pull request #579 from thefab/fix574

Fix #574 and a lot of test problems in some configurations