Speed-up gslb-prepare round #2 by potentially parallelizing some loops, removing dead code

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• First identify when .included files are not needed and eliminate as appropriate.
• Contemplate parallelizing loops. Check next links:
  https://toptechtips.github.io/2019-07-09-ansible_run_playbooks_tasks_in_parallel/
  https://toroid.org/ansible-parallel-dispatch
  https://blog.crisp.se/2018/01/27/maxwenzin/how-to-run-ansible-tasks-in-parallel

[alonsocamaro]

See https://devops.stackexchange.com/questions/3860/is-there-a-way-to-run-with-items-loops-in-parallel-in-ansible