Upgrade CI images to use Chrome V73
Attempt to solve issues such as https://gitlab.com/gitlab-org/gitlab-ce/issues/60953.
As mentioned in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27686#note_164692307, there may be some things that are related with the V73 and ChromeDriver update:
- Fixed a bug that caused ChromeDriver to fail on Linux devices without /dev/shm
- Made the HTTP server keep connection alive by default
- Increased HTTP server listening queue length