Reboot handler cleanup

> With toabctl@8399038 I fixed the possible race if you try to get the uptime from a host. Checking that the node is back in "ready" state is the next thing.
> Is there somewhere a list with possible node states?

In https://github.com/toabctl/barclamp-crowbar/commit/157e6353259c2e53ddc7001a1ca347914a41cfb8 I just assumed that a chef-client run always ends in "ready" or "problem" state. Otherwise the code has an endless loop. So please comment if this assumption is wrong.