Description of problem:
When you attempt to import a VM as a managed Host, but the underlying VM is already being managed by a different Host, the form allows you to click submit, but it throws no error, and gives no indication as to what happened. It simply stays on the same page. 

Version-Release number of selected component (if applicable):
6.14 - Snap 5

How reproducible:
100%

Steps to Reproduce:
1. Create a compute resource that has some VM associated.
2. Import this VM as a managed Host successfully.
3. Without disassociating or delete the first Host, attempt to import that VM as a managed Host again

Actual results:
When clicking 'Submit', you receive no error, and the page doesn't change at all.

Expected results:
There is some error thrown that indicates that this VM is already being managed by a Host

Additional info:
This was all done with a VMware compute resource, so it's possible the bug only affects this case.