Add retrying to rsync command.

This is specifically to target the case when the number of clients has
exceeded the server's 'max connections' setting. Instead of starting all over
again which is expensive, just retry this one command.
Add an error message if the metrics collector gets full.
Report the time since last succesful shipping.
Add a random offset to sleeping.

As barn-agents all get restarted at the same time on a host they can get into
sync. This change helps spread out their syncs over time instead of all happening
at the same time.
Add tar as a rollout mechanism.
Some updates to loggen.

Including sequence numbers which help verify no lost data.