Combine a maximum of options in the last test:
- Ansible Vault options from [GH-3338]
- raw_arguments
Note: it is not expected from Vagrant to reject incoherent combinations
- Don't mock the config object, but use a true instance
- When possible, take advantage of Rpsec before/after hooks to
reduce code repetitions
- Add an example ("with inventory_path option")
- Use a global variable to store the path of the generated inventory
- Miscellaneous changes in existing examples (style, fixes)