Comments in policy.json cause error in glance.

The glance package should create /etc/glance/policy.json when installed and so in general the version provided by this cookbook is not used. However is causes an error if used which this commit resolves.

/etc/glance/policy.json cannot be loaded if there are comments in the file, it must only contain JSON.

The exception raised is:
File "/usr/lib/python2.7/dist-packages/routes/middleware.py", line 132, in __call__
    response = self.app(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
    return resp(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 147, in __call__
    resp = self.call_func(req, *args, **self.kwargs)
  File "/usr/lib/python2.7/dist-packages/webob/dec.py", line 210, in call_func
    return self.func(req, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/glance/common/wsgi.py", line 532, in __call__
    request, **action_args)
  File "/usr/lib/python2.7/dist-packages/glance/common/wsgi.py", line 549, in dispatch
    return method(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/glance/api/v1/images.py", line 200, in detail
    self._enforce(req, 'get_images')
  File "/usr/lib/python2.7/dist-packages/glance/api/v1/images.py", line 140, in _enforce
    self.policy.enforce(req.context, action, {})
  File "/usr/lib/python2.7/dist-packages/glance/api/policy.py", line 102, in enforce
    self.load_rules()
  File "/usr/lib/python2.7/dist-packages/glance/api/policy.py", line 62, in load_rules
    rules = self._read_policy_file()
  File "/usr/lib/python2.7/dist-packages/glance/api/policy.py", line 89, in _read_policy_file
    self.policy_file_contents = json.loads(raw_contents)
  File "/usr/lib/python2.7/json/__init__.py", line 326, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python2.7/json/decoder.py", line 366, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python2.7/json/decoder.py", line 384, in raw_decode
    raise ValueError("No JSON object could be decoded")

This commit enforces the policy.json file defined by chef and does not allow a customised local version to be maintained. It also removes the comments from the policy.json file.

Fixes #110