recover from ending couch stream.

If the couch stream ends unexpectedly we'll retry to connect. This will
keep tapicero alive during a restart of the couch.
Do not clutter the logs if couch is down for longer

We count the retry events and only log the first ones, than every
minute, after 5 minutes, 10 minutes, halve an hour and every hour.
Merge pull request #2 from azul/feature/recover_from_end_of_stream

Recover from end of stream, retry until couch is back up