request-certificate: Handle JSON formatted responses

We have moved over to using JSON formatted error messages, rather than
html templates.

This fixes issue #26

request-certificate/caramelrequest/certificaterequest.py

@@ -168,7 +168,7 @@ def request_cert_from_server(self):
                 break
             else:
                 logging.error('Request failed: {}'
-                              .format(parse_html(response)))
+                              .format(parse(response)))
                 response.raise_for_status()
                 break
 
@@ -182,6 +182,14 @@ def printerr(text):
     sys.stderr.write(text + '\n')
 
 
+def parse(response):
+    try:
+        result = response.json()
+    except Exception:
+        result = parse_html(response)
+    return result
+
+
 def parse_html(response):
     return ''.join((e.text or '') + (e.tail or '')
                    for e in ET.fromstring(response.text).iterfind('body//'))