This brings down the test run from 108 sec to 15 sec.
There is an occasional port conflict because of the nature
the next port is chosen. So far it seems rare enough to live
with it.
Refactor tests that use testutil.WaitForResult to use retry.
Since this requires refactoring the test functions in general this patch
also shows the use of the github.com/pascaldekloe/goe/verify library
which provides a good mechanism for comparing nested data structures.
Instead of just converting the tests from testutil.WaitForResult to
retry the tests that performing a nested comparison of data structures
are converted to the verify library at the same time.
This adds two goroutines to perform autopilot tasks on the leader - one
to monitor the health of servers and another to periodically clean up
dead servers with a limit on removal count. Also adds a new http endpoint,
`/v1/operator/autopilot/health`, for querying this information through an
operator RPC endpoint.