bump max body post size for rebuilderd

roles/rebuilderd/templates/nginx.d.conf.j2

@@ -51,7 +51,7 @@ server {
     }
 
     location /api/v0/build/report {
-	    client_max_body_size 10M;
+	    client_max_body_size 20M;
 	    proxy_pass http://127.0.0.1:8484;
     }
 }