Replset tests

This PR reworks two replica set tests that were commented out during a refactor of the test suite.

I believe both of these tests describe expected behavior. Unfortunately, the two tests both currently fail (in the case of the former, the Mongo::Node representing the removed node doesn't seem to update its config, causing it to appear as a still-valid secondary; in the case of the latter, an connection-time query is sent with the op_timeout rather than the connect_timeout).

Both of these tests are representative of real-world failures we've observed in the past (the former occurred when we failed to change the hostname of an old replset member before removing it; the latter when an instance experienced disk failure, such that the kernel accepted connections but userspace was hung), so it's somewhat concerning to us that they're failing. Hopefully these issues can be fixed and the tests reincorporated so they don't regress again.