Fix tripleo-upgrade-hiera key deleting
Fix tripleo-upgrade-hiera key deleting

The commit fixes these issues:

* When tripleo-upgrade-hiera key deleting was used multiple times in a
  playbook, the fact tripleo_upgrade_hiera_data_del persisted from the
  previous invocation instead of getting gradually filled from empty
  dict. This resulted in never deleting the keys except on the first
  run of the task.

* When the key deleting was called in an Ansible `loop`, the external
  `item` variable and the internal `item` in the deleting code
  conflicted on naming, breaking the removal of the key. We now use
  `loop_var: upgrade_hiera_item` to avoid naming collisions.

Closes-Bug: #1832827
Change-Id: I3fa0717203f3f6eae852d019bec71e97eb485aa2

openstack/tripleo-common,openstack/tripleo-common