It runs too long in -short mode.

Disable the one in init, because it doesn't respect -short.

Make the part that claims to test execution in a finalizer
actually execute the test in the finalizer.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=aram.h, golang-codereviews, iant, khr
https://golang.org/cl/86550045