Follow-up from "Add option files for new DST and uDTS integration tests"

The following discussion from !1299 (merged) should be addressed:

• @graven started a discussion:

  for a future MR: we should change the way we do the above - specifically, we should follow the example below, where the persistreco_version is 'promoted' to a global variable by having a dedicated @configurable just to obtain it. Doing the same with input_process and dstformat, and then any function which needs to know their values can invoke those functions to look them up instead of those functions all needing their own dedicated bind -- thus simplifying the subsequent logic.