Improve error feedback

When an error occur instead of just return the HTTP response code the
client will now try to extract the error message that contains the reason
of the problem and show it to the user in a user-friendly way (no codes
at all), the intention of this patch is to improve the usability of the
ironic client. Things like HTTP response codes can still be viewed when
used with the debug mode enabled ( -d ).

Change-Id: Ieca021cc0e0eabe91c13335c3062ef9622da3004
Merge "Improve error feedback"