[CLOUDSTACK-10230] User is able to change to “Guest OS type” that has been removed

Users are able to change the OS type of VMs to “Guest OS type” that has been removed. This becomes a security issue when we try to force users to use HVM VMs (Meltdown/Spectre thing). A removed “guest os type” should not be usable by any users in the cloud.

Author: rafaelweingartner