Pass JSON to host_dns_check, fix issue with curl of harvester

Change-Id: I5b4dc9870e9c64f5a6ed77db787b6da096689ab6
diff --git a/roles/create-vms/tasks/main.yml b/roles/create-vms/tasks/main.yml
index 77244f0..8c1acb6 100644
--- a/roles/create-vms/tasks/main.yml
+++ b/roles/create-vms/tasks/main.yml
@@ -30,7 +30,7 @@
 - name: wait for VM name resolution
   when: on_maas
   host_dns_check:
-    hosts: "{{ head_vm_list | map(attribute='name') | list }}"
+    hosts: "{{ head_vm_list | map(attribute='name') | list | to_json }}"
     command_on_fail: "curl -sS --connect-timeout 3 -XPOST http://{{ harvester_ip.stdout }}:8954/harvest"
   register: all_resolved
   until: all_resolved.everyone == "OK"