Cephx keys are not picked up by "local_action: shell cat [...]"
when using ansible-vault encrypted keyrings.
This commit changes the logic to use the file lookup plugin and
extracts the key using jinja2 regex filters. The raw keys are then
set as ansible facts.

Closes-Bug: 1849127

Change-Id: Iacb1e42307c4de6a7a379e8cf279e073995fd5d3