Allow the task "Check parameters.yml" to fail gracefully (and continue)

The task "Check parameters.yml" is meant to register a variable to determine
if the task "Populate parameters.yml" should be run. So it should not
fail, but ignore any errors.
Additionally, the task "Check parameters.yml" is now set to use the .rc (returncode)
of the registered variable.

(side note: changed the old notation "action: template" to "template:")

--- finally a thought: The template module already only runs if the template is not already in place, or changed. Adding the "Check parameters" task has the side-effect of not updating the parameters.yml file automatically if the template changes. Perhaps this was intended, so I left it in place.