Don't fail if Virtual BMCs have already been created

Update the "Create the Virtual BMCs" task so that it doesn't fail when
a vbmc instance already exists. This avoids false failures that otherwise
occur if you re-run quickstart.

Closes-Bug: #1705734
Change-Id: Ib290fabd3b8ce868f189ad5bbd095fe996f39ce7

roles/undercloud-deploy/tasks/configure-vbmc.yml

@@ -73,10 +73,11 @@
 - name: Create the Virtual BMCs
   when: release not in ['liberty', 'mitaka', 'newton']
   command: "vbmc add {{ item.name }} --port {{ item.virtualbmc_port }} --libvirt-uri {{ vbmc_libvirt_uri }}"
+  args:
+    creates: /root/.vbmc/{{ item.name }}/config
   with_items: "{{ overcloud_nodes }}"
   become: true
   become_user: root
-  changed_when: false
 
 # TODO(lucasagomes): The service file should be included in the
 #                    virtualbmc RPM package.