Add multiversion support to packages api

This CL is the second installment in the
add-multiversion-uprev-support-to-pupr series. For the series finale,
we will be modifying the generator recipe to generate CLs using
the revised api. Stay tuned!

BUG=chromium:985035
TEST=unittest

Change-Id: I4665a1f08edb2e9368e308504797afd5831a16cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1796566
Tested-by: Yaakov Shaul <yshaul@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
diff --git a/api/controller/packages.py b/api/controller/packages.py
index 0443e74..12c8b7e 100644
--- a/api/controller/packages.py
+++ b/api/controller/packages.py
@@ -76,9 +76,12 @@
     # No uprevs executed, skip the output population.
     return
 
-  output_proto.version = result.new_version
-  for path in result.modified_ebuilds:
-    output_proto.modified_ebuilds.add().path = path
+  for modified in result.modified:
+    uprev_response = output_proto.responses.add()
+    uprev_response.version = modified.new_version
+    for path in modified.files:
+      uprev_response.modified_ebuilds.add().path = path
+
 
 
 @faux.all_empty