race in StatusHistoryTest

As seen here (though incorrectly targeted):
http://qa.jujucharms.com/releases/6015/job/run-unit-tests-race/attempt/3507#highlight

I was able to reproduce it locally, just by doing
cd cmd/juju/status
go test --race --check.v
^- unfortunately some of the earlier tests take 90s to complete, so this is a bit expensive (wall clock time is 222s for the whole suite, and a huge amount of time to build.)
Note that I also tried:
go test --race --check.v --check.f StatusHistorySuite

and that does *not* appear to trigger the failure.

==================
WARNING: DATA RACE
Write at 0x00000317e500 by goroutine 35:
  reflect.Value.Set()
      /snap/go/1016/src/reflect/value.go:1361 +0x106
  github.com/juju/testing.PatchValue()
      /home/jameinel/dev/go/src/github.com/juju/testing/patch.go:46 +0x195
  github.com/juju/testing.(*CleanupSuite).PatchValue()
      /home/jameinel/dev/go/src/github.com/juju/testing/cleanup.go:125 +0x5a
  github.com/juju/juju/cmd/juju/status_test.(*StatusHistorySuite).SetUpTest()
      /home/jameinel/dev/go/src/github.com/juju/juju/cmd/juju/status/history_test.go:34 +0x1b1
  runtime.call32()
      /snap/go/1016/src/runtime/asm_amd64.s:509 +0x3a
  reflect.Value.Call()
      /snap/go/1016/src/reflect/value.go:302 +0xc0
  gopkg.in/check%2ev1.(*suiteRunner).runFixture.func1()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:721 +0x184
  gopkg.in/check%2ev1.(*suiteRunner).forkCall.func1()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:666 +0x89

Previous read at 0x00000317e500 by goroutine 36:
  time.Now()
      /snap/go/1016/src/time/time.go:1049 +0xd3
  time.sendTime()
      /snap/go/1016/src/time/sleep.go:139 +0x44

Goroutine 35 (running) created at:
  gopkg.in/check%2ev1.(*suiteRunner).forkCall()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:663 +0x430
  gopkg.in/check%2ev1.(*suiteRunner).runFunc()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:673 +0x7e
  gopkg.in/check%2ev1.(*suiteRunner).runFixture()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:717 +0x7e
  gopkg.in/check%2ev1.(*suiteRunner).runFixtureWithPanic()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:735 +0xaa
  gopkg.in/check%2ev1.(*suiteRunner).forkTest.func1()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:760 +0x217
  gopkg.in/check%2ev1.(*suiteRunner).forkCall.func1()
      /home/jameinel/dev/go/src/gopkg.in/check.v1/check.go:666 +0x89

Goroutine 36 (running) created at:
  runtime.addtimerLocked()
      /snap/go/1016/src/runtime/time.go:122 +0xec
  context.WithDeadline()
      /snap/go/1016/src/context/context.go:401 +0x56c
  net.(*Dialer).DialContext()
      /snap/go/1016/src/net/dial.go:348 +0xe59
  net.(*Dialer).Dial()
      /snap/go/1016/src/net/dial.go:320 +0xa1
  net.DialTimeout()
      /snap/go/1016/src/net/dial.go:306 +0xb6
  gopkg.in/mgo%2ev2.resolveAddr.func1()
      /home/jameinel/dev/go/src/gopkg.in/mgo.v2/cluster.go:434 +0x72
==================