cluster: Make Vagrant optional

[Nuttymoon]

Allow defining a cluster to be deployed on remote machines, rather than virtual local ones.

To do:

• add an option to create (e.g. --remote)
• register the type of cluster in the config file (local vs remote)
• don't generate the Vagrantfile when not necessary
• update the documentation accordingly

[RReivax]

Change commands:

• start only works for local clusters with Vagrant: starts the machines and provision them if first time (--no-provision flag to only start the VMs). Starts all services.
• provision provisions the machines (local or remote cluster) by running the ansible-playbook command

We use the Ansible installed on the host machine instead of installing Ansible on an edge VM each time we create a cluster.