CFY-455 raise 404 when deployment does not exists on list executions
CFY-455 add test for 404 on listing executions for a non-existent deployment
CFT-455 add test for 404 when getting non existent execution
CFY-455 flake8
Merge pull request #8 from cloudify-cosmo/feature/CFY-455-error-when-needed

Verify execution exists on fetch events