bump diego-smoke-tests

Submodule src/github.com/cloudfoundry-incubator/diego-smoke-tests 6a4efe2..444d691:
  > run cf logs --recent before deleting

Signed-off-by: Atul Kshirsagar <atul.kshirsagar@gmail.com>
upgrade to Go 1.4

[finishes #84395302]

Signed-off-by: Atul Kshirsagar <atul.kshirsagar@gmail.com>