integration-cli: add more debugging for TestSwarmClusterRotateUnlockKey

[thaJeztah]

Relates to #38885 Flaky test: DockerSwarmSuite.TestSwarmClusterRotateUnlockKey

This test was updated in b79adac (#39616), but is still flaky #39883 (comment);

20:24:13  FAIL: docker_cli_swarm_test.go:1333: DockerSwarmSuite.TestSwarmClusterRotateUnlockKey
20:24:13
20:24:13  Creating a new daemon at: /go/src/github.com/docker/docker/bundles/test-integration/3/DockerSwarmSuite.TestSwarmClusterRotateUnlockKey
20:24:13  [d6f95e679cb65] waiting for daemon to start
20:24:13  [d6f95e679cb65] waiting for daemon to start
20:24:13  [d6f95e679cb65] daemon started
20:24:13
20:24:13  Creating a new daemon at: /go/src/github.com/docker/docker/bundles/test-integration/3/DockerSwarmSuite.TestSwarmClusterRotateUnlockKey
20:24:13  [d204a02ba4780] waiting for daemon to start
20:24:13  [d204a02ba4780] waiting for daemon to start
20:24:13  [d204a02ba4780] daemon started
20:24:13
20:24:13  [d204a02ba4780] joining swarm manager [d6f95e679cb65]@0.0.0.0:2477, swarm listen addr 0.0.0.0:2478
20:24:13  Creating a new daemon at: /go/src/github.com/docker/docker/bundles/test-integration/3/DockerSwarmSuite.TestSwarmClusterRotateUnlockKey
20:24:13  [d873d6a842829] waiting for daemon to start
20:24:13  [d873d6a842829] waiting for daemon to start
20:24:13  [d873d6a842829] daemon started
20:24:13
20:24:13  [d873d6a842829] joining swarm manager [d6f95e679cb65]@0.0.0.0:2477, swarm listen addr 0.0.0.0:2479
20:24:13  [d204a02ba4780] Stopping daemon
20:24:13  [d204a02ba4780] exiting daemon
20:24:13  [d204a02ba4780] Daemon stopped
20:24:13  [d204a02ba4780] waiting for daemon to start
20:24:13  [d204a02ba4780] waiting for daemon to start
20:24:13  [d204a02ba4780] daemon started
20:24:13
20:24:13  [d873d6a842829] Stopping daemon
20:24:13  [d873d6a842829] exiting daemon
20:24:13  [d873d6a842829] Daemon stopped
20:24:13  [d873d6a842829] waiting for daemon to start
20:24:13  [d873d6a842829] waiting for daemon to start
20:24:13  [d873d6a842829] daemon started
20:24:13
20:24:13  docker_cli_swarm_test.go:1413:
20:24:13      c.Assert(err, checker.IsNil, check.Commentf("%s", outs))
20:24:13  ... value *exec.ExitError = &exec.ExitError{ProcessState:(*os.ProcessState)(0xc000934240), Stderr:[]uint8(nil)} ("exit status 1")
20:24:13  ... Error response from daemon: rpc error: code = Unknown desc = The swarm does not have a leader. It's possible that too few managers are online. Make sure more than half of the managers are online.
20:24:13
20:24:13
20:24:13  [d6f95e679cb65] Stopping daemon
20:24:13  [d6f95e679cb65] exiting daemon
20:24:13  [d6f95e679cb65] Daemon stopped
20:24:13  [d204a02ba4780] Stopping daemon
20:24:13  [d204a02ba4780] exiting daemon
20:24:13  [d204a02ba4780] Daemon stopped
20:24:13  [d873d6a842829] Stopping daemon
20:24:13  [d873d6a842829] exiting daemon
20:24:13  [d873d6a842829] Daemon stopped

The interesting bit there is that the retry loop should have a 3 second sleep before retrying,
but looking at the failure above, the test started (and failed) within a second, which means that
a different error / output was returned.

This patch adds some additional debugging to that test to see if we can catch the reason
this test is still flaky.

[thaJeztah]

Logs from that failing test;

d6f95e679cb65.log
d204a02ba4780.log
d873d6a842829.log

[thaJeztah]

Failure on RS1 is #39857

https://ci.docker.com/public/blue/rest/organizations/jenkins/pipelines/moby/branches/PR-39885/runs/1/nodes/200/log/?start=0

[2019-09-09T20:37:36.900Z] ok  	github.com/docker/docker/daemon/logger	0.525s	coverage: 43.0% of statements
[2019-09-09T20:37:36.900Z] time="2019-09-09T20:37:35Z" level=info msg="Trying to get region from EC2 Metadata"
[2019-09-09T20:37:36.900Z] time="2019-09-09T20:37:36Z" level=info msg="Log stream already exists" errorCode=ResourceAlreadyExistsException logGroupName= logStreamName= message= origError="<nil>"
[2019-09-09T20:37:36.900Z] --- FAIL: TestLogBlocking (0.02s)
[2019-09-09T20:37:36.900Z]     cloudwatchlogs_test.go:313: Expected to be able to read from stream.messages but was unable to
[2019-09-09T20:37:36.900Z] time="2019-09-09T20:37:36Z" level=error msg=Error
[2019-09-09T20:37:36.900Z] time="2019-09-09T20:37:36Z" level=error msg="Failed to put log events" errorCode=InvalidSequenceTokenException logGroupName=groupName logStreamName=streamName message="use token token" origError="<nil>"
[2019-09-09T20:37:36.900Z] time="2019-09-09T20:37:36Z" level=error msg="Failed to put log events" errorCode=DataAlreadyAcceptedException logGroupName=groupName logStreamName=streamName message="use token token" origError="<nil>"
[2019-09-09T20:37:36.900Z] time="2019-09-09T20:37:36Z" level=info msg="Data already accepted, ignoring error" errorCode=DataAlreadyAcceptedException logGroupName=groupName logStreamName=streamName message="use token token"
[2019-09-09T20:37:36.900Z] FAIL
[2019-09-09T20:37:36.900Z] coverage: 78.2% of statements
[2019-09-09T20:37:36.900Z] FAIL	github.com/docker/docker/daemon/logger/awslogs	0.630s

[thaJeztah]

rebased; @cpuguy83 @tiborvass ptal

[thaJeztah]

rebased