Added hacking check for jsonutils

jsonutils provides some additional features in comparison to pure json
or simplejson modules. For example, on Python 2.6, it automatically
switches to simplejson that provides significant performance boost.

So let's enforce usage of the module in replacement to stdlib json.

Change-Id: I86ed6cd3316dd4da5e1b10b36a3ddba3739316d3
Merge "Added hacking check for jsonutils"