cmd/coordinator: nuke the reverse buildlet connection if close hangs.

Fixes golang/go#11869 I hope.

Change-Id: I84b5976e1dd5cf0f7dc8cd0171a283dd833adb18
Reviewed-on: https://go-review.googlesource.com/12632
Reviewed-by: Andrew Gerrand <adg@golang.org>
1 file changed