As part of the bug below, this can be used to make sure the
playbooks generated from the heat output can be iterated over
using the loop variable.
This adds a pre-processor for upgrade_tasks that adds a "when
step == N" condition based on the value of the tags. That is
"tags: step1" becomes "when: step == 1". When there is an
existing when statement the new step condition is appended.
Change-Id: Ief593dc758a2ffe33c1cbcbda9289393fcf023e4
Related-Bug: 1708115