add OUTPUT_FILE='foo.log' env variable support to test.sh script.

Side consequence of this is that `make test-smoke` can become interactive again.

scripts/test.sh

@@ -46,6 +46,11 @@ export ETCD_VERIFY=all
 source ./scripts/test_lib.sh
 source ./scripts/build.sh
 
+if [ -n "${OUTPUT_FILE}" ]; then
+  log_callout "Dumping output to: ${OUTPUT_FILE}"
+  exec > >(tee -a "${OUTPUT_FILE}") 2>&1
+fi
+
 PASSES=${PASSES:-"fmt bom dep build unit"}
 PKG=${PKG:-}