Add warning dialog on RHEV host restart

Issue

• RFE - RHEV-M should warn us if we going to restart VMs by accident
• When an admin restarts a host through the "power management" feature without putting it into maintenance mode all the VMs which are hosted on that host going to be stopped (not shut-downed) without any warning.
• The warning message only says:

"Are you sure you want to Restart the following Host(s)?
host05.mycompany.org"

• A more accurate message would be:

"This will stop (not gracefully) the following VMs:
vm1.mycompany.org
vm3.mycompany.org

Are you sure you want to Restart the following Host(s)?
host05.mycompany.org"

• When an admin restarts a host through the "power management" feature without putting it into maintenance mode all the VMs which are hosted on that host going to be stopped without any warning. The customer would like to get a warning that the running VMs on that host will get killed.
• To prevent killing guest by accident which would cause outage and interfere with business.