rubygem-staypuft:  Assigning hosts to deployment - during the assignment all the buttons should be disabled.

Environment:


Steps to reproduce:
1. Install rhel-osp-installer.
2. Create an HAneutron deployment.
3. Assign 3 controllers at once.


Result:
The assignment takes more than several seconds. During this time the user is able to select other hosts and click on the "Assign Hosts" button.

Expected result:
All the buttons should  become unavailable during the assignment to avoid confusion.