Refactor project to extract common operations

[diogobaeder]

Currently, as is, the project has some duplicated code between different distributions (centos and debian), and there's a gap between the progress of our debian roles and the centos ones (there are many more roles for debian, today, since we have more active developers who are more acquainted with debian-like distros). This is a problem, since it hinders the evolution of our centos roles, and requires more effort to implement features for all our supported distributions.

So what we have to do is think about a way to have a helping structure to be able to extract common procedures between different distros, and let them specialize these procedures where they need. By doing this, we'll be able to have features for different distributions for free, when they're implemented.

Not sure which version this should go into, though. Maybe 0.7.0, because it sounds to me as too big a change to go into 0.6.0, and we want to ship 0.6.0 as soon as possible, since there are many bugfixes and new features to release (mainly security ones).