Convert the tasks/* directories to roles

[KellerFuchs]

There is a bunch of refactors this would enable:

• use role-specific handlers;
• make roles call one another (which would let us avoid duplicated code).

Moreover, roles are the standard mechanism for code reuse in Ansible, and it should make it easier for people to reuse our configs.

[KellerFuchs]

@hashbang/administrators Any objection?

[RyanSquared]

Sounds good, no objection here.