intermittent failure in apiserver/facades/agent/storageprovisioner/internal/filesystemwatcher

[Tim Penhey]

FAIL: watchers_test.go:142: WatchersSuite.TestWatchMachineManagedFilesystemsVolumeAttachmentDead

watchers_test.go:161:
    wc.AssertChangeInSingleEvent()
/workspace/src/github.com/juju/juju/state/testing/watcher.go:191:
    c.Assert(actual, gc.HasLen, 0)
... obtained []string = []string{"1", "2"}
... n int = 0

[Tim Penhey (thumper)]

https://github.com/juju/juju/pull/8454