Data race in service package.

[russjones]

Found the following data race in 9359f6d running go test -race -v ./... -check.f=TestAudit on our macOS cloud box.

==================
WARNING: DATA RACE
Write at 0x000005c087e0 by goroutine 39:
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).RemoveService()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:128 +0x1c6
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).serve.func1()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:152 +0x242

Previous read at 0x000005c087e0 by goroutine 38:
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).serve.func1()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:147 +0x1c0

Goroutine 39 (running) created at:
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).serve()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:144 +0x91
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).Start()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:166 +0x125
  github.com/gravitational/teleport/integration.(*TeleInstance).Start()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/integration/helpers.go:607 +0x33b
  github.com/gravitational/teleport/integration.(*IntSuite).newTeleportWithConfig()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/integration/integration_test.go:152 +0x43c
  github.com/gravitational/teleport/integration.(*IntSuite).TestAuditOff()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/integration/integration_test.go:1558 +0x11c
  runtime.call32()
      /usr/local/go/src/runtime/asm_amd64.s:509 +0x3a
  reflect.Value.Call()
      /usr/local/go/src/reflect/value.go:302 +0xc0
  github.com/gravitational/teleport/vendor/gopkg.in/check%2ev1.(*suiteRunner).forkTest.func1()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/vendor/gopkg.in/check.v1/check.go:763 +0x9b0
  github.com/gravitational/teleport/vendor/gopkg.in/check%2ev1.(*suiteRunner).forkCall.func1()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/vendor/gopkg.in/check.v1/check.go:657 +0x89

Goroutine 38 (running) created at:
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).serve()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:144 +0x91
  github.com/gravitational/teleport/lib/service.(*LocalSupervisor).Start()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/lib/service/supervisor.go:166 +0x125
  github.com/gravitational/teleport/integration.(*TeleInstance).Start()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/integration/helpers.go:607 +0x33b
  github.com/gravitational/teleport/integration.(*IntSuite).newTeleportWithConfig()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/integration/integration_test.go:152 +0x43c
  github.com/gravitational/teleport/integration.(*IntSuite).TestAuditOff()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/integration/integration_test.go:1558 +0x11c
  runtime.call32()
      /usr/local/go/src/runtime/asm_amd64.s:509 +0x3a
  reflect.Value.Call()
      /usr/local/go/src/reflect/value.go:302 +0xc0
  github.com/gravitational/teleport/vendor/gopkg.in/check%2ev1.(*suiteRunner).forkTest.func1()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/vendor/gopkg.in/check.v1/check.go:763 +0x9b0
  github.com/gravitational/teleport/vendor/gopkg.in/check%2ev1.(*suiteRunner).forkCall.func1()
      /tmp/teleport-tests/src/github.com/gravitational/teleport/vendor/gopkg.in/check.v1/check.go:657 +0x89
==================