Rename playbook variables

[IamLunchbox]

@meffie Would you be fine if I'd overhaul the used variables in create.yml and so forth? Working with them got me all confused, due to their shortness and unclear meaning (ra, rc, p and so forth).

[meffie]

I originally had longer names, but changed them to be more terse to try to make the yaml more readable. Perhaps they are too terse.