Description of problem:
Error 404 is displayed after MigrationPolicy deletion.

Version-Release number of selected component (if applicable):
4.12

How reproducible:
always

Steps to Reproduce:
1. Go to Virtualization > MigrationPolicies
2. Create a migration policy as an admin or a privileged user,
if there is no any migration policy
3. Try to delete the migration policy

Actual results:
The following text is displayed:
404: Page Not Found
The server doesn't have a resource type "migr". Try refreshing the page if it was recently added.

Expected results:
The remaining list of migration policies or the page with the button to create a migration policy is displayed.

Additional info:
It does not matter from where a migration policy is deleted (from the list or when being in its details page).