test: add temporary show_skips flag.
test: add temporary show_skips flag.

To find test files with legacy headers.

We can remove this flag once everything is converted.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5694060
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go