Replace int variables with 0/1 as only possible values with bools,
where possible.

Change-Id: I958c082e703bbc1540309da3e17612fc8e247932
Reviewed-on: https://go-review.googlesource.com/105036
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>