Try iso-8859-1 decode if utf8 fails

Technically, the BMC is in error returning non-utf8 encoded content,
however, of *course* some BMCs fail to do so.  Fallback to iso-8859-1
which will probably have bad data in a value somewhere, but it won't
break the entire parsing.

Change-Id: Id7c3c507a0eeb4c31ca52cfadf6ac77deefa3869

pyghmi/util/webclient.py

@@ -253,8 +253,11 @@ class SecureHTTPConnection(httplib.HTTPConnection, object):
                 # gzip
                 pass
         if rsp.status >= 200 and rsp.status < 300:
-            if body and not isinstance(body, str):
-                body = body.decode('utf8')
+            if body and not isinstance(body, type(u'')):
+                try:
+                    body = body.decode('utf8')
+                except Exception:
+                    body = body.decode('iso-8859-1')
             return json.loads(body) if body else {}, rsp.status
         return body, rsp.status