Named Stratum1 Replicas

This introduces Stratum1 replicas with an (optional) name different from the fully qualified repository name.
Using this new feature, we can have more than one Stratum1 repository for each Stratum0 repository on a single host. Additionally it is now possible to have Stratum1 replicas on the same host as the associated Stratum0 repository.

*Note:* Since this feature is extremely handy for testing the replication functionality, this Pull Request also adapts the Stratum1 integration tests.