[devtools] Avoid db_cache collisions and mis-loading This is done by stopping to share the db_cache between TestDataBaseHandler instances It may seem overkill, but is the only way I could get it to work properly. I think the whole db caching code needs some rework to better work with different db handlers. Closes #4601328

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−cubicweb-web: embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js