fb_storage always ignores override files when '_clowntown_override_file_method' not defined

[jaymzh]

According to both the docs and the logs, '_clowntown_override_file_method' allows you to add additional restrictions to when override files take effect, but if it's not defined, then they always take effect.

Turns out, this isn't true, we always return false. This is a simple bug, but fixing it it probably requires a slow rollout to FB so I haven't sent a PR.

Docs:

For additional safety, you can define a check method in
`node['fb_storage']['_clowntown_override_file_method']`
that will be invoked whenever override files are evaluated.

Actual code where we say we're ignore the method, but then returnf alse.

      def override_file_applies?(verb, fname, quiet = false)
        if File.exist?(fname)
          base_msg = "fb_storage: System has #{fname} file present"
          if node['fb_storage']['_clowntown_override_file_method']
            ...
          end
          unless quiet
            Chef::Log.warn(
              "#{base_msg} but the override check method is not defined, " +
              'therefore we are ignoring it.',
            )
          end
          return false   # this should be `true`
        end
        return false
      end