webadmin: mutually exclude HA and non-migratable in UI

In the VM popup dialog - user would not be able to select both
High-Availability and 'don't allow migration' or 'allow only manual
migration'. this was done because HA mode requires the ability to
automatically migrate the VM.

the action is also blocked by the beckend

Change-Id: I04a1e8641c41394d021bcb4bb323c987111609ea
Signed-off-by: Ofri Masad <omasad@redhat.com>