Clarify config file code to be clear that it handles directories. ...

… Add a check for IsRegular() before reading a config path.  Add a comment
about exec.Command("hostname", "-f").
Merge pull request #215 from thockin/cleanups

Clarify config file code to be clear that it handles directories, too.  ...
Merge pull request #216 from thockin/logging

Minor: log cleanups
Logging cleanup in Kubelet

Make it easier to see the signal when looking at kubelet logs.  Make the
signal more consistent and legible.