Return specific error codes where possible

We use Unix errno values where it makes sense.  Print the stack trace
and return 255 when we have an internal error.  We will need to return
more specific errors from jclouds and jclouds-karaf for this commit to
work well.  References #36.
Merge pull request #40 from maginatics/exit-codes-1.5.x

Return specific error codes where possible