cmd/coordinator: initialize inStaging again
cmd/coordinator: initialize inStaging again

It got lost at some point.

Change-Id: I50f262d971ce4de418dbb5ee4f0ddd383ce72d0e
Reviewed-on: https://go-review.googlesource.com/21616
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build