tests-prepare-*: Use local connection to perform actions on localhost

Use 'connection: local' in the test-prepare-containers.yml and
test-prepare-host.yml playbooks similar to the test-prepare-keys.yml
playbook one.

Change-Id: I1e69b72121ac07f23a467c61b9ab5888fc57c275

test-prepare-containers.yml

@@ -15,6 +15,7 @@
 
 - name: Playbook for creating containers
   hosts: localhost
+  connection: local
   become: true
   gather_facts: true
 

test-prepare-host.yml

@@ -15,6 +15,7 @@
 
 - name: Playbook for configuring hosts
   hosts: localhost
+  connection: local
   become: true
   pre_tasks:
     - include: "common-tasks/test-set-nodepool-vars.yml"
@@ -32,6 +33,7 @@
 
 - name: Playbook for configuring the LXC host
   hosts: localhost
+  connection: local
   become: true
   roles:
     - role: "lxc_hosts"