Improve youtube-dl logging

[dop251]

When trying to deploy podsync on a DigitalOcean droplet, I faced with this error:

youtube-dl error: /tmp/podsync-119127838/17gpOMhVlas.%(ext)s error="failed to execute youtube-dl: exit status 1"

There was nothing more in the log that would allow to diagnose the problem further which was not very helpful. This PR makes it a bit easier by explicitly logging a message if a '429 Too Many Requests' error was detected or otherwise dumping the stdout from the youtube-dl command.

(Side note in case someone finds this by googling the error: turns out that due to DO's unique IPv6 allocation policy the /64 block ends up being shared by multiple droplets. Most likely Google considers a /64 block as one user (as it should be) and applies combined rate limits to it. The remedy here is to force IPv4).

[mxpv]

(Side note in case someone finds this by googling the error: turns out that due to DO's unique IPv6 allocation policy the /64 block ends up being shared by multiple droplets. Most likely Google considers a /64 block as one user (as it should be) and applies combined rate limits to it. The remedy here is to force IPv4).

Thanks, that's good to know. I think i'll start building FAQ for things like this.

[mxpv]

Thanks!