Raise a ConnectionError, so we can catch it

scanners are expecting a ConnectionError exception on failure,
so let's make sure we raise that, and don't break scanning.
diff --git a/src/plugins/utils/jsonapi.py b/src/plugins/utils/jsonapi.py
index ecda530..bd10a8c 100644
--- a/src/plugins/utils/jsonapi.py
+++ b/src/plugins/utils/jsonapi.py
@@ -47,7 +47,7 @@
             return get(url, cookie = cookie, auth = auth, token = token, retries = retries)
     if rv.status_code < 400:
         return rv.json()
-    raise Exception("Could not fetch JSON, server responded with status code %u" % rv.status_code)
+    raise requests.exceptions.ConnectionError("Could not fetch JSON, server responded with status code %u" % rv.status_code, response = rv)
 
 def gettxt(url, cookie = None, auth = None):
     """ Same as above, but returns as text blob """