Stop AsyncZmqActor gracefully

[amper43]

we should stop actor's asyncio event loop gracefully by sigterm signal

https://github.com/hastic/hastic-server/blob/master/analytics/analytics/utils/concurrent.py#L130
https://github.com/hastic/hastic-server/blob/master/analytics/analytics/utils/concurrent.py#L71

[rozetko]

Related issue: https://github.com/hastic/hastic-server/issues/493