Update code_generator template to latest centos

RE: https://github.com/opscode/chef-dk/issues/177
Merge pull request #212 from martinb3/update_centos

Update code_generator template to latest centos
Improve debugging of HTTP errors for `chef push`

Without the `-D` flag you now will see an error message like:

```
Error: Failed to push policy to the server
Reason: Net::HTTPServerException: HTTP 400 Bad Request: Field 'name'
invalid
```

When the `-D` flag is given, the request and response will be shown in a
format roughly similar to the actual HTTP messages sent and received,
including headers and message bodies.
Extract common code for nested exceptions
Add nested exception features to install command
Move service exception inspectors to separate files