Race condition on Monitor.globalTags

[gwossum]

Race condition detected in test on Monitor.globalTags for 1.x branch:

==================
WARNING: DATA RACE
Write at 0x00c00341def0 by goroutine 348:
  runtime.mapassign_faststr()
      /go/src/runtime/map_faststr.go:203 +0x0
  github.com/influxdata/influxdb/monitor.(*Monitor).SetGlobalTag()
      /go/pkg/mod/github.com/influxdata/[email protected]/monitor/service.go:189 +0xd1
  github.com/influxdata/plutonium/cmd/influxd/run.(*Server).init()
      /root/project/cmd/influxd/run/server.go:871 +0xbc
  github.com/influxdata/plutonium/cmd/influxd/run.(*Server).appendClusterService.func1()
      /root/project/cmd/influxd/run/server.go:311 +0x34
  github.com/influxdata/plutonium/cluster.(*Service).processJoinClusterRequest()
      /root/project/cluster/service.go:1178 +0x338
  github.com/influxdata/plutonium/cluster.(*Service).handleConn()
      /root/project/cluster/service.go:489 +0xd90
  github.com/influxdata/plutonium/cluster.(*Service).handleMuxConn.func3()
      /root/project/cluster/service.go:312 +0x9e

Previous read at 0x00c00341def0 by goroutine 179:
  runtime.mapiterinit()
      /go/src/runtime/map.go:815 +0x0
  github.com/influxdata/influxdb/monitor.(*Monitor).Statistics()
      /go/pkg/mod/github.com/influxdata/[email protected]/monitor/service.go:320 +0x1ae
  github.com/influxdata/influxdb/monitor.(*Monitor).storeStatistics()
      /go/pkg/mod/github.com/influxdata/[email protected]/monitor/service.go:443 +0x72e
  github.com/influxdata/influxdb/monitor.(*Monitor).Open.func1()
      /go/pkg/mod/github.com/influxdata/[email protected]/monitor/service.go:126 +0x39

Goroutine 348 (running) created at:
  github.com/influxdata/plutonium/cluster.(*Service).handleMuxConn()
      /root/project/cluster/service.go:310 +0x2e9
  github.com/influxdata/plutonium/cluster.(*Service).serveMux.func1()
      /root/project/cluster/service.go:264 +0x9e

Goroutine 179 (running) created at:
  github.com/influxdata/influxdb/monitor.(*Monitor).Open()
      /go/pkg/mod/github.com/influxdata/[email protected]/monitor/service.go:126 +0x43d
  github.com/influxdata/plutonium/cmd/influxd/run.(*Server).Open()
      /root/project/cmd/influxd/run/server.go:683 +0x92a5
  github.com/influxdata/plutonium/cmd/influxd/run.(*Command).Run()
      /root/project/cmd/influxd/run/command.go:184 +0x173c
  github.com/influxdata/plutonium/cmd/testhelper.(*TestDataRunCommand).MustRun.func1()
      /root/project/cmd/testhelper/integration.go:488 +0xde
==================