runtime: reduce delays in finalizer test.
runtime: reduce delays in finalizer test.

The runtime tests are executed 4 times in all.bash
and there is currently a 5-second delay each time.

R=golang-dev, minux.ma, khr, bradfitz
CC=golang-dev
https://codereview.appspot.com/42450043

pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go