UI: hot set number of CPU when updating a VM

* allow updating the number of sockets of a runing VM
* disable number of cores per sockets change
* disable total number of cpus change
* added a icon which explains about the action taken when changing the
* values.

Any change to the socket field will recalculate the total CPUs.
This means we add/remove whole sockets from a VM.

Changing the topology, i.e. the number of CPUs per socket is not allowed
as it can not be reflected in a live OS.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1036777
Change-Id: Ieac0e757c54b002eeab8f9099e6e8d151eb43340
Signed-off-by: Roy Golan <rgolan@redhat.com>