Include all packages in the Buildroot compose variant.

Buildroot includes every packages in the Koji tag except
of those which are already in other compose variants.

In order for it to work, the additional_packages need
to be set to * for Buildroot.

Signed-off-by: Jan Kaluza <jkaluza@redhat.com>

shared/additional_and_filter_packages.conf

@@ -78,6 +78,11 @@ additional_packages = [
             "git-all",
         ]
     }),
+    ("^Buildroot$", {
+        "*": [
+            "*",
+        ]
+    }),
 ]