Increment CRI version from v1alpha1 to v1alpha2

This also incorporates the version string into the package name so
that incompatibile versions will fail to connect.

Arbitrary choices:
- The proto3 package name is runtime.v1alpha2. The proto compiler
  normally translates this to a go package of "runtime_v1alpha2", but
  I renamed it to "v1alpha2" for consistency with existing packages.
- kubelet/apis/cri is used as "internalapi". I left it alone and put the
  public "runtimeapi" in kubelet/apis/cri/runtime.

hack/update-generated-runtime-dockerized.sh

@@ -19,7 +19,7 @@ set -o nounset
 set -o pipefail
 
 KUBE_ROOT=$(dirname "${BASH_SOURCE}")/..
-KUBE_REMOTE_RUNTIME_ROOT="${KUBE_ROOT}/pkg/kubelet/apis/cri/v1alpha1/runtime/"
+KUBE_REMOTE_RUNTIME_ROOT="${KUBE_ROOT}/pkg/kubelet/apis/cri/runtime/v1alpha2/"
 source "${KUBE_ROOT}/hack/lib/init.sh"
 
 kube::golang::setup_env