autotest: Add hostinfo support for platform keyval

BUG=b:116258296
TEST=None

Change-Id: I5c5dd0f511c7f086fc66cb976e89280d08c726a6
Reviewed-on: https://chromium-review.googlesource.com/1309014
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/tko/models.py b/tko/models.py
index ddb073b..d8be245 100644
--- a/tko/models.py
+++ b/tko/models.py
@@ -342,8 +342,10 @@
     # TODO(ayatane): Investigate if urllib.quote is better.
     label_string = ','.join(label.replace(':', '%3A')
                             for label in hostinfo.labels)
-    # TODO(ayatane): Check if host-platform is also needed.
-    return {'host-labels': label_string}
+    return {
+            'host-labels': label_string,
+            'host-platform': hostinfo.model,
+    }
 
 
 class patch(object):