On my laptop, I'm currently seeing a huge number of intermittent test
failures all related to WaitForLeader returning after the test node has
become a leader, but before it has actually finished starting up, in
particular, performing the serf/Raft reconciliation.
Waiting for the index to become nonzero makes the tests pass reliably,
by also blocking until the new leader has started committing state.
Armon Dadgar