Add CRI release build

Add installation scripts needed to generate CRI + CNI tar package on
release.
Update Github action release script to generate CRI release tarballs for
Linux and Windows.

Signed-off-by: Derek McGowan <derek@mcg.dev>

script/setup/install-cni-windows

@@ -0,0 +1,97 @@
+#!/bin/bash
+
+#   Copyright The containerd Authors.
+
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+
+#       http://www.apache.org/licenses/LICENSE-2.0
+
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+
+set -eu -o pipefail
+
+destdir="${destdir:-"C:\\Program Files\\containerd"}"
+WINCNI_BIN_DIR="${destdir}/cni"
+WINCNI_PKG=github.com/Microsoft/windows-container-networking
+WINCNI_VERSION=aa10a0b31e9f72937063436454def1760b858ee2
+
+go get -d "${WINCNI_PKG}/..."
+cd "${GOPATH}/src/${WINCNI_PKG}"
+git checkout "${WINCNI_VERSION}"
+make all
+install -D -m 755 "out/nat.exe" "${WINCNI_BIN_DIR}/nat.exe"
+install -D -m 755 "out/sdnbridge.exe" "${WINCNI_BIN_DIR}/sdnbridge.exe"
+install -D -m 755 "out/sdnoverlay.exe" "${WINCNI_BIN_DIR}/sdnoverlay.exe"
+
+CNI_CONFIG_DIR="${destdir}/cni/conf"
+mkdir -p "${CNI_CONFIG_DIR}"
+
+# split_ip splits ip into a 4-element array.
+split_ip() {
+  local -r varname="$1"
+  local -r ip="$2"
+  for i in {0..3}; do
+    eval "$varname"[$i]=$( echo "$ip" | cut -d '.' -f $((i + 1)) )
+  done
+}
+
+# subnet gets subnet for a gateway, e.g. 192.168.100.0/24.
+calculate_subnet() {
+  local -r gateway="$1"
+  local -r prefix_len="$2"
+  split_ip gateway_array "$gateway"
+  local len=$prefix_len
+  for i in {0..3}; do
+    if (( len >= 8 )); then
+      mask=255
+    elif (( len > 0 )); then
+      mask=$(( 256 - 2 ** ( 8 - len ) ))
+    else
+      mask=0
+    fi
+    (( len -= 8 ))
+    result_array[i]=$(( gateway_array[i] & mask ))
+  done
+  result="$(printf ".%s" "${result_array[@]}")"
+  result="${result:1}"
+  echo "$result/$((32 - prefix_len))"
+}
+
+# nat already exists on the Windows VM, the subnet and gateway
+# we specify should match that.
+gateway="$(powershell -c "(Get-NetIPAddress -InterfaceAlias 'vEthernet (nat)' -AddressFamily IPv4).IPAddress")"
+prefix_len="$(powershell -c "(Get-NetIPAddress -InterfaceAlias 'vEthernet (nat)' -AddressFamily IPv4).PrefixLength")"
+
+subnet="$(calculate_subnet "$gateway" "$prefix_len")"
+
+# The "name" field in the config is used as the underlying
+# network type right now (see
+# https://github.com/microsoft/windows-container-networking/pull/45),
+# so it must match a network type in:
+# https://docs.microsoft.com/en-us/windows-server/networking/technologies/hcn/hcn-json-document-schemas
+bash -c 'cat >"'"${CNI_CONFIG_DIR}"'"/0-containerd-nat.conf <<EOF
+{
+    "cniVersion": "0.2.0",
+    "name": "nat",
+    "type": "nat",
+    "master": "Ethernet",
+    "ipam": {
+        "subnet": "'$subnet'",
+        "routes": [
+            {
+                "GW": "'$gateway'"
+            }
+        ]
+    },
+    "capabilities": {
+        "portMappings": true,
+        "dns": true
+    }
+}
+EOF'