Exception raised when importing prefix against duplicate vlan_vid

[candlerb]

Issue type: bug report

Python version: 3.5.2
NetBox version: 2.0.6

To reproduce:

Import two VLANs with same vid:

vid,name,status
301,test1,Reserved
301,test2,Reserved

Import a prefix which references this vid

prefix,status,vlan_vid
192.0.2.0/24,Active,301

This causes a Server Error:

<class 'ipam.models.MultipleObjectsReturned'>

get() returned more than one VLAN -- it returned 2!

I think in this case Netbox is correct - it should either reject the upload, or import the prefix with a NULL vlan association and generate a warning. But it would be better to report this properly rather than throw an exception (which mails a backtrace to the administrator)