Make ConnectivityTest faster and more informative

When one of the Atlas connectivity tests is failing, it's slow and annoying to figure out which of the Atlas test connection strings is actually failing. This is because:

1. We run the same test once for each URI, and the test results files just overwrite each other
2. In order to make sure that all the tests run, we have to use --rerun-tasks, which makes the tests slow

We can fix both these problems by:

1. Pass all the Atlas connection strings in to a single run of each ConnectivityTest, perhaps as a delimited list in a new system property, and
2. Refactor each ConnectivityTest to be parameterized, and include the connection string (without credentials) as part of the test name, so that they are unique.