Reduce 'flakiness' of Action test on worker Filter

worker/uniter/filter_test.go no longer cares what order Actions arrive
in.  We think that indeterminate latency might account for occasional
out-of-order errors in this test.
Merge pull request #312 from binary132/flaky-action-queue-test-fix

Reduce 'flakiness' of Action test on worker Filter

worker/uniter/filter_test.go no longer cares what order Actions arrive
in.  We think that indeterminate latency might account for occasional
out-of-order errors in this test.