Revive RAPI QA tests for 2.0-style RAPI

This patch fixes the RAPI QA tests to work with today's RAPI code and
also does some other minor improvements:
  - QA: only create the cluster if so configured (‘create-cluster’ key),
    this allows running parts of the QA suite against existing clusters
  - export the “hvparams” for instances in RAPI

Reviewed-by: imsnah