Remove 'fold' from barn-agent loop.

The fold makes the code safer but I think it is at the cost of
the code being readable for someone new to the project. I've
removed it to hopefully make the steps easier to see.

This change also ensures that barn-agent doesn't failover when it's got a
'flacky' connection i.e. where it's managing to ship some files out of the
entire list. In production barn-agent can often end up running like this.

@omidaladini @johnglover 
Well it's not documented, because it's new :D

Imagine a hypothetical situation where one was running a lot of barn-agents in production where it was not possible to disable barn on a per service basis. We would want a quick way of disabling an errant service.