Refactor existing roles, put timemaster inside a role

[eroussy]

This PR refactors the existing roles to be compliant with ansible-galaxy. It also refactors the centos prerequis to use the debian prerequisites roles.

vm_manager, python3-setup-ovs, cukinia and cukinia tests are now deployed inside their own roles. Timemaster have its own role and is moved outside the network playbook

API changes:

• The network playbook no longer configures snmp and timemaster. The roles should be called alone, or using the main playbook