Closes #2567 flaky it tests

[diasf]

Reasons for flakiness:

• Async indexing, solr didn't yet index all documents before tests started already querying it
• Non-atomic filesystem operations (file deletion not yet observable before checking absence)
• Async mail notifications
• Jenkins specific: Test containers (solr & postgres) are started for both dataverse-persistence and dataverse-webapp in the same docker network. The test containers are only stopped and removed at the end of the verify maven lifecylce. This means that during the execution of dataverse-webapp integration tests, there are 2 solr and 2 postgres containers running with the same DNS name respectively. Less of a problem with postgres as tests rollback their transactions. But for solr this caused some issues as the solrclient, when sending requests to http://solr:8983, was getting responses from one or the other container. To circumvent this, the 2 test containers are now started before verify and then cleaned up when verify finishes.

Issue: #2567