We will use this code to execute the code in some process' network
namespace.
I did the vendoring a bit differently, as gvt seems to be a bit dumb
about getting dependencies for test packages (it tried to vendor
ginkgo and gomega, since cni tests are using it).
Also, instead of vendoring golang.org/x/sys as
github.com/containernetworking/cni/vendor/golang.org/x/sys I moved it
to scope's vendor directory.
