Track VM hypervisor host

[ebusto]

Environment

• Python version: 3.5.4
• NetBox version: 2.4.7

Proposed Functionality

It would be useful to track which physical device a VM resides on.

Use Case

In the case where a VM is not automatically migrated from one VM cluster member to another (such as with VMware vSphere's vMotion functionality), it would be quite useful to know which VMs would be impacted by a device failing or requiring maintenance.

Database Changes

One additional virtual machine field, which would be optional, along with a validation to ensure the device is a member of the cluster hosting the VM.

External Dependencies

None.

[ebusto]

This also provides a mechanism to capture the relationship between bare-metal servers and their parent devices.

[jeremystretch]

This was discussed at length in #142 during the original implementation. The current model was largely agreed upon and likely won't be substantially changed in the near future.

[ebusto]

That's unfortunate, considering how trivial a change this is.