Virtual machine serializer does not require cluster assignment

[jeremystretch]

Environment

• Python version: 3.5.2
• NetBox version: 2.4.7

Steps to Reproduce

Attempt to create a new virtual machine via the REST API with no cluster assignment:

curl -X POST \
-H "Authorization: Token <token>" \
-H "Content-Type: application/json" \
-H "Accept: application/json; indent=4" \
http://localhost:8000/api/virtualization/virtual-machines/ \
--data '{"name": "test-vm1"}'

Expected Behavior

The response should indicate that the cluster field is required.

Observed Behavior

The request yields an IntegrityError exception.