Raise error instead of returning empty.

[jvanderaa]

Fixes #223

I believe this fixes the returning of no devices when access is denied. Working on getting the tests written for this.

[joewesch]

This was implemented by @FragmentedPacket pre-fork due to this issue raised: netbox-community/ansible_modules#312.

I think we should consider the implications of both requests to determine if we want to revert this.

[jvanderaa]

We should revert this @joewesch, from https://docs.ansible.com/ansible/latest/dev_guide/developing_inventory.html:

The specifics will vary depending on API and structure returned. Remember that if you get an inventory source error or any other issue, you should raise AnsibleParserError to let Ansible know that the source was invalid or the process failed.

[jvanderaa]

What I'm trying to figure out here yet is how to test the changes

[joewesch]

The only inventory tests that we currently have are comparison tests. I don't think you need to create a new testing methodology as part of this PR.