Expand r_id to resource_id for more clarity

While working on documentation for the Resource class, I came back upon
the `r_id` name that exists on a bunch of methods. The name is an
argument to a bunch of public methods, so I think it should be as self
explanatory as possible.

Change-Id: I45c83c2f88f3cff6e3eb516c431183336a0b3201
Merge "Expand r_id to resource_id for more clarity"