cmd/release: shut down VMs after 1 hour
cmd/release: shut down VMs after 1 hour

Change-Id: Iaadc436d3d694b7f91e27d1c1c262e48879a82fd
Reviewed-on: https://go-review.googlesource.com/5250
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,evandbrown/build,evandbrown/build,proppy/build,golang/build,golang/build,proppy/build,proppy/build,proppy/build,evandbrown/build,golang/build