Build a small package and immediatelly filter out all binary RPMs

Because mbs build system  currently does not support building empty modules.

python3.yaml

@@ -32,3 +32,17 @@ data:
         community: https://www.python.org/
         documentation: https://docs.python.org/3/
         tracker: https://src.fedoraproject.org/modules/python3
+    filter:
+        rpms:
+            - python-rpm-macros
+            - python-srpm-macros
+            - python2-rpm-macros
+            - python3-rpm-macros
+            - platform-python-rpm-macros
+    components:
+        rpms:
+            python-rpm-macros:
+                rationale: |
+                    Build and filter all RPMs, since an empty module doesn't
+                    build
+                ref: master