Add service template publication

The publication of service may require several virtual machine templates.

The template creation must be a dedicated tool:

• take a mandatory --type argument with only 2 possibles values vm or service
• take a mandatory --template argument for the template
• take an optional --group argument to set the template group
• take an optional --mode argument to set the permissions (VM or service, for VM, we should set the recursive parameter to make sure the disk has the proper permissions too).

The service template should contains some template strings to be resolved at runtime for the vm_template attribute:

  "roles": [
    {
      "name": "server",
      "cardinality": 1,
      "vm_template": ##VM_TEMPLATE(foo-bar)##

must lookup the virtual machine template foo-bar to get its ID and replace it in the service template.

NB: the template strings specification is not mandatory and can be changed if better format is found.