Add YAML missing dashes at start of file

YAML files are supposed to start with three dashes to indicate the
beginning of the document.
Nota: Ansible won’t complain if they are missing.

Change-Id: I5cd417971f7af2977e7527b7b454a999718cfcda

ansible/roles/memcached/handlers/main.yml

+---
 - name: Restart memcached container
   vars:
     service: "{{ memcached_services.memcached }}"

ansible/roles/rally/handlers/main.yml

+---
 - name: Restart rally container
   vars:
     service_name: "rally"

ansible/roles/tempest/handlers/main.yml

+---
 - name: Restart tempest container
   vars:
     service_name: "tempest"

ansible/roles/vmtp/handlers/main.yml

+---
 - name: Restart vmtp container
   vars:
     service_name: "vmtp"