Use uuid4 to generate slave client_id (#895)
Use uuid4 to generate slave client_id (#895)

Fixes #894 

Current implementation collides easily in environments with large number of slave processes on the same host starting at the same time.
locustio/locust,mbeacom/locust,heyman/locust,mbeacom/locust,mbeacom/locust,locustio/locust,locustio/locust,locustio/locust,mbeacom/locust