PCT-637: Query Analytics does not handle MySQL Restart

http://tools-ci.percona.com/job/percona-agent-branch/28/console
I'm not sure about this. My idea was to simply give more room for listener - it could be doing something else, e.g. rotating slow log and catching later on MySQL restarts.
I mean it can block, simply not waiting on `select` https://github.com/percona/percona-agent/blob/PCT-637_check_for_mysql_restart/qan/manager.go#L282 but doing something inside of any of the `case` statements e.g. here https://github.com/percona/percona-agent/blob/PCT-637_check_for_mysql_restart/qan/manager.go#L311 In such case goroutine isn't waiting on select, so it can't pickup immediately.
Also if listener is falling behind  I didn't want to limit queue to just remembering one MySQL restart in case listener wanted to know how many restarts were made.

Anyway I think all this is kinda rare cases so I can change that.

But I don't understand the idea of changing `default` to `time.After(1*time.Second)`. With `default` first message will land on channel and second will immediately fail. With `time.After(1*time.Second)` first message will land on channel and second will fail after one second - not that much difference. Just asking because maybe you meant buffer size 0? Unbuffered channel? This would make more sense as it would give one second to pick up first message.