newvm: Fix vCPU count/CPU model

Although the `newvm.sh` script had a `--vcpus` argument, its value was
never being used.

The `--cpu host` argument for `virt-install` is deprecated in favor of
`--cpu host`.

newvm.sh

@@ -171,7 +171,8 @@ set -- \
     --name ${name} \
     --metadata title=${hostname} \
     --memory ${memory} \
-    --cpu host \
+    --vcpus ${vcpus} \
+    --cpu host-model \
     --location ${location} \
     --extra-args "${extra_args}" \
     --disk pool=default,size=${disk_size},cache=none \