Make compute VMs specs configurable for 3-nodes scenario

Replicate what was made for the va-hci scenario.

scenarios/reproducers/3-nodes.yml

@@ -42,9 +42,9 @@ cifmw_libvirt_manager_configuration:
       sha256_image_name: "{{ cifmw_discovered_hash }}"
       image_local_dir: "{{ cifmw_basedir }}/images/"
       disk_file_name: "centos-stream-9.qcow2"
-      disksize: 50
-      memory: 8
-      cpus: 4
+      disksize: "{{ [cifmw_libvirt_manager_compute_disksize|int, 50] | max }}"
+      memory: "{{ [cifmw_libvirt_manager_compute_memory|int, 8] | max }}"
+      cpus: "{{ [cifmw_libvirt_manager_compute_cpus|int, 4] | max }}"
       nets:
         - public
         - osp_trunk