[17.06] Fix possible data race in manager/state/store/memory_test.go

[thaJeztah]

Backport of #2537 for 17.06

git checkout -b 17.06-backport-2536-data-race upstream/bump_v17.06
git cherry-pick -s -S -x 06add13d57411618c18d4b9d181013e932462834

no conflicts, cherry-pick was clean

This PR is a fix for #2536, essentially using the first proposed way of fixing the original issue.

This fixes a possible data race in manager/state/store/memory_test.go

An alternative to this fix would be to define a new variable in the following way:

    for c := 0; c != 5; c++ {
        ...
        x := c
        go func() {
            ...
            Name: nodeIDs[i%benchmarkNumNodes] + "_" + strconv.Itoa(x) + "_" + strconv.Itoa(i),
            ...
        }
    }

[thaJeztah]

Heh. The irony; it's failing on another data race;

WARNING: DATA RACE
Read at 0x00c42032a7a0 by goroutine 147:
  github.com/docker/swarmkit/manager/dispatcher.(*Dispatcher).isRunning()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/manager/dispatcher/dispatcher.go:413 +0x4b
  github.com/docker/swarmkit/manager/dispatcher.(*Dispatcher).Heartbeat()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/manager/dispatcher/dispatcher.go:1102 +0xcd
  github.com/docker/swarmkit/api.(*authenticatedWrapperDispatcherServer).Heartbeat()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/api/dispatcher.pb.go:471 +0x17d
  github.com/docker/swarmkit/api.(*raftProxyDispatcherServer).Heartbeat()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/api/dispatcher.pb.go:1727 +0x290
  github.com/docker/swarmkit/api._Dispatcher_Heartbeat_Handler.func1()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/api/dispatcher.pb.go:1008 +0xa1
  github.com/docker/swarmkit/vendor/github.com/grpc-ecosystem/go-grpc-prometheus.UnaryServerInterceptor()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/vendor/github.com/grpc-ecosystem/go-grpc-prometheus/server.go:29 +0xc9
  github.com/docker/swarmkit/api._Dispatcher_Heartbeat_Handler()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/api/dispatcher.pb.go:1010 +0x1fb
  github.com/docker/swarmkit/vendor/google.golang.org/grpc.(*Server).processUnaryRPC()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/vendor/google.golang.org/grpc/server.go:638 +0x10cc
  github.com/docker/swarmkit/vendor/google.golang.org/grpc.(*Server).handleStream()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/vendor/google.golang.org/grpc/server.go:796 +0x18a4
  github.com/docker/swarmkit/vendor/google.golang.org/grpc.(*Server).serveStreams.func1.1()
      /home/ubuntu/.go_workspace/src/github.com/docker/swarmkit/vendor/google.golang.org/grpc/server.go:449 +0xb6
....

[codecov]

Codecov Report

Merging #2697 into bump_v17.06 will increase coverage by 4.34%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           bump_v17.06    #2697      +/-   ##
===============================================
+ Coverage        57.72%   62.07%   +4.34%     
===============================================
  Files               10       42      +32     
  Lines             1230     5716    +4486     
===============================================
+ Hits               710     3548    +2838     
- Misses             451     1820    +1369     
- Partials            69      348     +279

[thaJeztah]

closing, as 17.06 is EOL