[FEATURE] Variables to refactor

[andrespias]

The names of the role variables could be confused with the backuppc_server role. Also, is missing the prefix backuppc_ in backup_state and include_files

[ulvida]

Indeed. However, the refactor of variables will lead to a change of the major version of the role.

Moreover the names, let's also analyse the whole role to see if it can be improved.

Particularly, we should take into consideration the problem raised in PR when addressing the issue #2.

[ulvida]

Also, is missing the prefix backuppc_ in backup_state and include_files

This is addressed in v2.0.0.
However, I missed the problem of possible variables duplication with role backuppc_server. We should address this when refactoring this role. I put an issue.