source: allow passing all apt::keyring attributes

This uses the same logic as apt::keyring itself, and what I think would
be the least surprising logic:

1. Passing both `dir` and `filename`: you have provided the full path,
   so that is used in the signed-by setting.
2. Passing just the `filename` means you want to use the default dir,
   /etc/apt/keyrings.
3. Passing just the `dir` means you want to use the given directory, and
   the `name` attribute as the filename.
4. Passing only `name` means use `name` with the default dir.

Author: kenyon

manifests/source.pp

@@ -186,14 +186,20 @@
         ensure   => $_key_ensure,
         content  => $_key['content'],
         source   => $_key['source'],
+        dir      => $_key['dir'],
         filename => $_key['filename'],
+        mode     => $_key['mode'],
         before   => $_before,
       }
-      # TODO replace this block with a reference to the apt::keyring's final filename/full_path
-      if $_key['filename'] {
-        $_list_keyring = $_key['filename']
+
+      $_list_keyring = if $_key['dir'] and $_key['filename'] {
+        "${_key['dir']}${_key['filename']}"
+      } elsif $_key['filename'] {
+        "/etc/apt/keyrings/${_key['filename']}"
+      } elsif $_key['dir'] {
+        "${_key['dir']}${_key['name']}"
       } else {
-        $_list_keyring = "/etc/apt/keyrings/${_key['name']}"
+        "/etc/apt/keyrings/${_key['name']}"
       }
     }
   } else {