Fix import collection marks and signatures

The import code was unable to link up a collection version with its
metadata because using multiple fields as a foreign key is not supported
by django-import-export. The only viable fallback given existing export
files is to use the upstream_id.

fixes #1836

(cherry picked from commit 4cf073b)

CHANGES/1836.bugfix

@@ -0,0 +1 @@
+Fixed import failing to associate signatures and marks with their collection version.

pulp_ansible/app/modelresource.py

@@ -138,6 +138,19 @@ def set_up_queryset(self):
         """
         return CollectionVersionSignature.objects.filter(pk__in=self.repo_version.content)
 
+    def before_import_row(self, row, **kwargs):
+        """
+        Finds and sets collection version using upstream_id.
+
+        Args:
+            row (tablib.Dataset row): incoming import-row representing a single content.
+            kwargs: args passed along from the import() call.
+        """
+        super().before_import_row(row, **kwargs)
+
+        cv = CollectionVersion.objects.get(upstream_id=row["signed_collection"])
+        row["signed_collection"] = str(cv.pk)
+
     class Meta:
         model = CollectionVersionSignature
         import_id_fields = ("pubkey_fingerprint", "signed_collection")
@@ -155,6 +168,19 @@ def set_up_queryset(self):
         """
         return CollectionVersionMark.objects.filter(pk__in=self.repo_version.content)
 
+    def before_import_row(self, row, **kwargs):
+        """
+        Finds and sets collection version using upstream_id.
+
+        Args:
+            row (tablib.Dataset row): incoming import-row representing a single content.
+            kwargs: args passed along from the import() call.
+        """
+        super().before_import_row(row, **kwargs)
+
+        cv = CollectionVersion.objects.get(upstream_id=row["marked_collection"])
+        row["marked_collection"] = str(cv.pk)
+
     class Meta:
         model = CollectionVersionMark
         import_id_fields = ("value", "marked_collection")