runtime: disable TestSetPanicOnFault for dragonfly/386
runtime: disable TestSetPanicOnFault for dragonfly/386

This test currently deadlocks on dragonfly/386.

Update issue 7421

LGTM=minux.ma
R=golang-codereviews, minux.ma
CC=golang-codereviews
https://codereview.appspot.com/69380043

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang