1008808: json ValueErrors have no .msg attribute

In cases where we expect a json body on an error
response, we try to parse it, and catch any exceptions
if it's not valid and ignore. Except we were attempting
to log the ValueError.msg, which doesn't exist, raising
an AttributeError.
Merge pull request #97 from candlepin/alikins/1008808_fix_json_parse

1008808: json ValueErrors have no .msg attribute