cmd/coordinator: put go repo in its own directory inside tmp

Previously the Go repo would be in /tmp/watcher1234 and each sub repo in
/tmp/watcher1234/subrepo. This change puts the Go repo inside
/tmp/watcher1234/go.

Change-Id: I4dc3d9fad8cc41647f6a821273565b815fc0f968
Reviewed-on: https://go-review.googlesource.com/18240
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed