If the metrics break interval happened to occur between first and second
worker starting up and getting connected to the cluster, the test
would fail because the second worker didn't get a chance to connect and
send data. The test now waits for the cluster setup to complete
before workers send metrics data.
- Some baselines for tests in "leaks" group were outdated.
- Changed a few of the cluster/communication tests to terminate
more explicitly instead of relying on btest-bg-wait to kill
processes. This makes the tests finish faster in the success case
and makes the reason for failing clearer in the that case.
