Use runtime instead of datetime for test output.

test/utils/shippable/timing.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+
+import sys
+import time
+
+start = time.time()
+
+for line in sys.stdin:
+    seconds = time.time() - start
+    sys.stdout.write('%02d:%02d %s' % (seconds // 60, seconds % 60, line))

test/utils/shippable/timing.sh

@@ -1,5 +1,5 @@
-#!/bin/bash -eux
+#!/bin/bash -eu
 
 set -o pipefail
 
-"$@" 2>&1 | gawk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; fflush(); }'
+"$@" 2>&1 | "$(dirname "$0")/timing.py"