Fix and document more dynamic fields in Request.
action #2432 - Refactor the repo checker to look for broken dependencies in staging prjs

First approach to this.  In this version we create a execution_plan
where there are one (for now) fallback if the plan fails.

If the logic is correct, needs to be refactored a lot:

- Plans are combination of different repos, we need to priorize
  certain repos over the rest, or explore all the combinations.

- execution_plan is using as index the main repo, this is confusing.

- The overall code is confusing and unordered, with creation of
  fields dynamically in the Request class, like goodrepo, goodrepos,
  downloads, etc.  This needs to be done in an ordered way