Intermittent test failure - PresenceSuite.TestWatchPeriod

[Tim Penhey]

FAIL: presence_test.go:256: PresenceSuite.TestWatchPeriod

[LOG] 71.85107 INFO juju state/presence: Faking presence to time slot 0
[LOG] 71.85109 INFO juju state/presence: Not faking presence time. Real time slot in use.
presence_test.go:275:
    assertChange(c, ch, presence.Change{"a", true})
presence_test.go:66:
    c.Fatalf("watch reported nothing, want %v", want)
... Error: watch reported nothing, want {a true}

OOPS: 11 passed, 1 FAILED
--- FAIL: TestPackage (7.60 seconds)
FAIL
FAIL launchpad.net/juju-core/state/presence 7.787s

I had this fail two or three times in a row running all the tests from root using "go test ./..."

I then went into the state/presence directory and ran the tests, all passed twice, moved back up to state, and ran all the tests from there, passed twice in a row, then back up to the project root, and the tests passed again twice in a row.

It seems to be very timing based, so should be looked at.