Use map_async and get to avoid a deadlock
Wrap gtk3cairo test in try except
Forcefully terminate

If process did not return within 5 sec assume that it is hanging and forcefully terminate
Catch the right error
Merge pull request #3741 from jenshnielsen/14_backend_testing

BLD : Add time out to looking up backends in setup.py

Make sure that backend testing in multiprocessing is done with a timeout