new --exit-on-disconnect flag to start lbrynet, will exit process when connection drops

[eukreign]

No description provided.

[moodyjon]

Can you please rebase or use some other technique to simplify the change? Things like 54da1e3 and 4f9c98e have already been submitted.

[coveralls]

Coverage remained the same at 57.78% when pulling 8bd7008 on exit_on_disconnect into a334a93 on master.

[moodyjon]

General comment about sleep_delay and _urgent_need_reconnect:

    async def network_loop(self):
        sleep_delay = 30
        while self.running:
            await asyncio.wait(
                [asyncio.sleep(30), self._urgent_need_reconnect.wait()], return_when=asyncio.FIRST_COMPLETED   #### It seems like this should be sleep(sleep_delay), or min(sleep_delay, X) not a fixed 30s.
            )
            if self._urgent_need_reconnect.is_set():
                sleep_delay = 30
            self._urgent_need_reconnect.clear()   #### Should this be moved after "if not client:" so that the urgent reconnect will still be needed? When cleared here, the urgency goes away until another RPC is tried and finds the connection is not available.
            if not self.is_connected:
                client = await self.connect_to_fastest()
                if not client:
                    log.warning("failed to connect to any spv servers, retrying later")
                    sleep_delay *= 2
                    sleep_delay = min(sleep_delay, 300)
                    continue
                log.debug("get spv server features %s:%i", *client.server)

[moodyjon]

You should consider adding SystemExit exception handling here:

lbry-sdk/lbry/extras/cli.py

Line 281 in a334a93

except (GracefulExit, KeyboardInterrupt, asyncio.CancelledError):

I guess the risk is that it would hang while shutting down components, but calling daemon.stop() is done in other scenarios like SIGINT, SIGTERM.