Office tests are using outdated images

We build a custom image for the office tests, using the servlet engine image name and tag to prevent rebuilding it every time. However, the tag is not a good oracle as it can be as generic as "latest", in which case the tag is just never updated even if the image itself has changed...
As a matter of fact it appears that we apparently rely on the same tomcat:latest image for 3 years in our CI agents for the test.

We should rely instead on a hash of the image.