Fuel agent versioning and upgrade

As a fuel operator, I want to be able to smoothly manage already existing environments (aka clusters) at least in terms of adding new nodes. That implies that current provisioning engine must be capable of working with versioned input data as well and must support which was already done in nailgun provisioning serializers.

Therefore, the enhanced and robust versioning for fuel-agent objects and data driver structures in addition to already existent cloud-init templates versioning must be implemented.