Move set_up_logging to the front (#130).

When the repo is instantiated, custom cmdb code might use logging,
so logging should already be configured.
Set log-level of root logger to ERROR.

By means of this the format and further attempts to reset  the loglevels succeed.
fix *_end hooks being passed an empty node list

thanks @mfriedenhagen
Merge pull request #131 from mfriedenhagen/issue-130

Move set_up_logging to the front (#130).