Error reporting POST to Product error

When there is an error in the product or variants that are sent via post to the Product endpoint, the error message is structured in a way that the underlying pyactiveresource.connection.ResourceInvalid object cannot decode it properly, which leads to a very un-informative error.
Please see stacktrace below:

Traceback (most recent call last):
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\connection.py", line 286, in _open
    http_response = self._handle_error(self._urlopen(request))
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\connection.py", line 318, in _urlopen
    return urllib.request.urlopen(request)
  File "C:\Python34\lib\urllib\request.py", line 161, in urlopen
    return opener.open(url, data, timeout)
  File "C:\Python34\lib\urllib\request.py", line 469, in open
    response = meth(req, response)
  File "C:\Python34\lib\urllib\request.py", line 579, in http_response
    'http', request, response, code, msg, hdrs)
  File "C:\Python34\lib\urllib\request.py", line 507, in error
    return self._call_chain(*args)
  File "C:\Python34\lib\urllib\request.py", line 441, in _call_chain
    result = func(*args)
  File "C:\Python34\lib\urllib\request.py", line 587, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 422: Unprocessable Entity

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\activeresource.py", line 824, in save
    data=self.encode())
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\connection.py", line 364, in post
    return self._open('POST', path, headers=headers, data=data)
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\shopify\base.py", line 23, in _open
    self.response = super(ShopifyConnection, self)._open(*args, **kwargs)
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\connection.py", line 288, in _open
    http_response = self._handle_error(err)
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\connection.py", line 414, in _handle_error
    raise ResourceInvalid(err)
pyactiveresource.connection.ResourceInvalid: Response(code=422, body="b'{"errors":{"base":["The variant \'Antique Bronze \\/ Ice pattern\' already exists. Please change at least one option value."]}}'", headers={'X-XSS-Protection': '1; mode=block; report=/xss-report?source%5Baction%5D=create&source%', 'X-Frame-Options': 'DENY', 'X-Stats-UserId': '0', 'X-Content-Type-Options': 'nosniff', , 'Date': 'Wed, 06 Sep 2017 17:17:23 GMT', 'Strict-Transport-Security': 'max-age=7776000', 'X-Stats-ApiPermissionId': '42905249', 'X-Sorting-Hat-PodId-Cached': '0', 'Content-Security-Policy': "default-src 'self' data: blob: 'unsafe-inline' 'unsafe-eval' https://* shopify-pos://*; block-all-mixed-content; child-src 'self' https://* shopify-pos://*; connect-src 'self' wss://* https://*; script-src https://cdn.shopify.com https://checkout.shopifycs.com https://js-agent.newrelic.com https://bam.nr-data.net https://dme0ih8comzn4.cloudfront.net https://api.stripe.com https://mpsnare.iesnare.com https://appcenter.intuit.com https://www.paypal.com https://maps.googleapis.com https://stats.g.doubleclick.net https://www.google-analytics.com https://visitors.shopify.com https://v.shopify.com https://widget.intercom.io https://js.intercomcdn.com 'self' 'unsafe-inline' 'unsafe-eval'; upgrade-insecure-requests; report-uri /csp-report?source%5Baction%5D=create&source%5Bapp%5D=Shopify&source%5Bcontroller%5D=admin%2Fproducts&source%5Bsection%5D=admin_api&source%5Buuid%5D=5e3df701-e2e3-4b70-bda3-b7d15592a0f5", 'X-Sorting-Hat-ShopId-Cached': '0', 'Connection': 'close', 'Referrer-Policy': 'origin-when-cross-origin', 'X-Request-Id': '5e3df701-e2e3-4b70-bda3-b7d15592a0f5', 'X-Shopify-Shop-Api-Call-Limit': '1/40', 'Content-Type': 'application/json; charset=utf-8', 'Server': 'nginx', 'X-ShardId': '15', 'X-Dc': 'ash', 'Transfer-Encoding': 'chunked', 'X-Download-Options': 'noopen', 'X-Permitted-Cross-Domain-Policies': 'none', 'HTTP_X_SHOPIFY_SHOP_API_CALL_LIMIT': '1/40', 'X-Sorting-Hat-PodId': '15', 'X-Sorting-Hat-Section': 'pod'}, msg="Unprocessable Entity")

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\user\Dropbox\virtualenvs\lighting\xologic_connection\product.py", line 692, in create_on_shopify
    success = new_product.save()
  File "C:\Users\user\Dropbox\virtualenvs\lighting\lib\site-packages\pyactiveresource\activeresource.py", line 832, in save
    self.errors.from_json(err.response.body)
AttributeError: 'list' object has no attribute 'from_json'
```
The relevant error is 
`body="b'{"errors":{"base":["The variant \'Antique Bronze \\/ Ice pattern\' already exists. Please change at least one option value."]}}'", `

It would be nice to get just that.

Start at xologic_connection/product.py line 692 and trace the save and error-handling path through the pyactiveresource stack shown in the report. Reproduce the 422 response for an invalid product or duplicate variant, then verify that the underlying Shopify validation message is exposed instead of the AttributeError.