Make playbook compatible with multiple installations on same host

[guidograzioli]

fix #9

Limitations:

• host must have nodename assigned as they will form a cluster
• playbooks must use roles: [ <role> ] instead of include_role because of https://docs.ansible.com/ansible/latest/user_guide/playbooks_reuse_roles.html#passing-different-parameters

Summary of changes:

• added jdg_nodename parameter for specifying instance name in cluster
• added jdg_port_offset param to specify alternate ports
• added missing cache_config param specification in arguments_spec
• updated converge and verify molecule setup

[rpelisse]

LGTM!

[rpelisse]

@guidograzioli lgtm! Please merge and rebase at your earliest convenience :)