Race in github.com/juju/juju/state/workers

[Curtis Hovey]

As seen at
    http://reports.vapour.ws/releases/issue/58cace8e749a5604ffa821a1

WARNING: DATA RACE
Write by goroutine 112:
  github.com/juju/juju/state.(*State).SetClockForTesting()
      /home/ubuntu/juju-core_2.2-alpha1/src/github.com/juju/juju/state/state.go:2158 +0x3e
  github.com/juju/juju/state_test.(*MigrationSuite).SetUpTest()
      /home/ubuntu/juju-core_2.2-alpha1/src/github.com/juju/juju/state/modelmigration_test.go:36 +0x29a
  runtime.call32()
      /usr/lib/go-1.6/src/runtime/asm_amd64.s:472 +0x3d
  reflect.Value.Call()
      /usr/lib/go-1.6/src/reflect/value.go:303 +0xcd
  gopkg.in/check%2ev1.(*suiteRunner).runFixture.func1()
      /home/ubuntu/juju-core_2.2-alpha1/src/gopkg.in/check.v1/check.go:721 +0x1b8
  gopkg.in/check%2ev1.(*suiteRunner).forkCall.func1()
      /home/ubuntu/juju-core_2.2-alpha1/src/gopkg.in/check.v1/check.go:666 +0x80

Previous read by goroutine 202:
  github.com/juju/juju/state.(*State).getLeadershipLeaseClient()
      /home/ubuntu/juju-core_2.2-alpha1/src/github.com/juju/juju/state/state.go:409 +0x151
  github.com/juju/juju/state.newWorkers.func4()
      /home/ubuntu/juju-core_2.2-alpha1/src/github.com/juju/juju/state/workers.go:52 +0x69
  gopkg.in/juju/worker%2ev1.(*Runner).runWorker()
      /home/ubuntu/juju-core_2.2-alpha1/src/gopkg.in/juju/worker.v1/runner.go:478 +0x546

This was introduced by
    https://github.com/juju/juju/commit/059183e53e552f6a4dac273e896c110f502ab692