Follow-up to CL 37270.

This considerably reduces the time to run the test.

Before:

real	0m7.638s
user	0m14.341s
sys	0m2.244s

After:

real	0m4.867s
user	0m7.107s
sys	0m1.842s

Change-Id: I8837a5da0979a1c365e1ce5874d81708249a4129
Reviewed-on: https://go-review.googlesource.com/37461
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Munday <munday@ca.ibm.com>