Extract shared discover plugin logic into the step

Author: therazix

docs/releases/pending/4391.fmf

@@ -0,0 +1,6 @@
+description: |
+  The :ref:`/plugins/discover/shell` discover plugin now supports
+  the ``path`` and ``url-content-type`` keys, which are handled
+  in the same way as in the :ref:`/plugins/discover/fmf` discover
+  plugin. The plugin now also correctly installs test dependencies
+  specified in the ``require`` and ``recommend`` keys.

tmt/schemas/discover/shell.yaml

@@ -26,10 +26,19 @@ properties:
     $ref: "/schemas/core#/definitions/summary"
 
   url:
+    $ref: "/schemas/common#/definitions/fmf_id/properties/url"
+
+  url-content-type:
     type: string
+    enum:
+      - git
+      - archive
 
   ref:
-    type: string
+    $ref: "/schemas/common#/definitions/fmf_id/properties/ref"
+
+  path:
+    $ref: "/schemas/common#/definitions/fmf_id/properties/path"
 
   dist-git-source:
     $ref: "/schemas/common#/definitions/dist-git-source"