Description of problem:
Attach and Detach action shows no flash message, just redirects to an instance page 

Version-Release number of selected component (if applicable):
5.8.0.16

How reproducible:
Always

Steps to Reproduce:
1. Go Compute -> Cloud -> Instances
2. Click Configuration -> Attach a Cloud Volume to this Instance
3. Choose any available volume from drop-down list, clisk "Save"

Actual results:
After the click on save button, nothing happens for several seconds, then redirection to initial instance page without result message appeared

Expected results:
After click on "Save" button, then comes up the redirection to instance page with result (flash) message 

Additional info:
The initial action performed anyway, so it attaches/detaches, just shows no message