[6.10] Failing backup tests

[vsedmik]

In Satellite 6.10, 13 out of 20 backup tests are failing due to two reasons:

1. With transition from pulp2 to pulp3 the mongoDB was replaced by postgres, while we still expect 'mongo_data.tar.gz' and '.mongo.snar' present in the backup.
2. Dynflowd and foreman-tasks services are not present in 6.10, while some tests try to stop them before taking the backup. We need to check if they were replaced or dropped entirely.