Don't log call errors for 204 response codes

[smarquard]

In utils/mhttpclient.py, an error is logged if a request gets a response code that is not 200:

if status_code != 200:
if self.logger:
self.logger.error('call error in %s, status code {%r}: %s',
urlparse.urlunparse(url), status_code, b.getvalue())
raise IOError, 'Error in Matterhorn client'

However the GC dashboard returns status code 204, and as the docs/scripts/run_dashboard_push.py uses mhttpclient, GC logs are filled up with:

galicaster 2014-07-23 10:53:31,707 ERROR mhhttpclient call error in http://media.uct.ac.za/dashboard/rest/agents/jamesc/snapshot.png, status code {204}:

As 204 is not an error code, mhttpclient should not log an error when receiving it.

[hcaloto]

Thank you Stephen