Panic during replay-live

[nathanielc]

I can reliably reproduce a panic close of closed channel when performing replay-live actions.

panic: close of closed channel

goroutine 201 [running]:
panic(0xb82b60, 0xc820bea0a0)
        /usr/lib/go/src/runtime/panic.go:481 +0x3e6
github.com/influxdata/kapacitor.(*Edge).Close(0xc820e676c0)
        /home/nathanielc/projects/kapacitor/src/github.com/influxdata/kapacitor/edge.go:121 +0x1c6
github.com/influxdata/kapacitor/services/replay.(*Service).doReplay.func1(0xc820a27380, 0xc820213a40)
        /home/nathanielc/projects/kapacitor/src/github.com/influxdata/kapacitor/services/replay/service.go:1186 +0x124
github.com/influxdata/kapacitor/services/replay.(*Service).doReplay(0xc8200eb760, 0xc820a753e0, 0x24, 0xc820213a40, 0xc820a8e720, 0x7f67513e88b0, 0xc820e62930)
        /home/nathanielc/projects/kapacitor/src/github.com/influxdata/kapacitor/services/replay/service.go:1194 +0x29b
github.com/influxdata/kapacitor/services/replay.(*Service).doLiveBatchReplay(0xc8200eb760, 0xc820a753e0, 0x24, 0xc820213a40, 0x7f6751470058, 0xc820a7b860, 0xc820cda001, 0xecdaf285c, 0x27c61c74, 0x14962a0, ...)
        /home/nathanielc/projects/kapacitor/src/github.com/influxdata/kapacitor/services/replay/service.go:1129 +0x136
github.com/influxdata/kapacitor/services/replay.(*Service).handleReplayBatch.func1(0xc8200eb760, 0xc820ae98c0, 0xc820213a40, 0x7f6751470058, 0xc820a7b860, 0xc820a753e0, 0x24, 0x0, 0x0, 0xc820be9740, ...)
        /home/nathanielc/projects/kapacitor/src/github.com/influxdata/kapacitor/services/replay/service.go:1006 +0xb9
created by github.com/influxdata/kapacitor/services/replay.(*Service).handleReplayBatch
        /home/nathanielc/projects/kapacitor/src/github.com/influxdata/kapacitor/services/replay/service.go:1008 +0x8cd