Integration test failure: TestDemoteToSingleManager

[aaronlehmann]

Saw the failure here: https://circleci.com/gh/docker/swarmkit/5056

--- FAIL: TestDemoteToSingleManager (5.11s)
    Error Trace:    integration_test.go:294
    Error:      Received unexpected error "rpc error: code = 13 desc = transport is closing"

cc @LK4D4

[aaronlehmann]

Have an error message now:

--- FAIL: TestDemoteToSingleManager (68.92s)
    Error Trace:    integration_test.go:103
            integration_test.go:290
    Error:      Received unexpected error node 641qbawnuunrlrnypp7yppuh1 had different roles in spec and certificate, WORKER and MANAGER respectively
            github.com/docker/swarmkit/manager/state/raft/testutils.PollFuncWithTimeout
                /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/manager/state/raft/testutils/testutils.go:74: polling failed

[aaronlehmann]

Integration tests seem to run reliably after the work done for #1826. Closing.