add build for flannel-io/flannel-cni-plugin

Dockerfile

@@ -1,11 +1,13 @@
 ARG ARCH="amd64"
-ARG TAG="v0.9.1"
+ARG TAG="v1.0.0"
+ARG FLANNEL_CNI_TAG="v1.0"
 ARG UBI_IMAGE=registry.access.redhat.com/ubi7/ubi-minimal:latest
 ARG GO_IMAGE=rancher/hardened-build-base:v1.16.7b7
 
 ### Build the cni-plugins ###
 FROM ${GO_IMAGE} as cni_plugins
 ARG TAG
+ARG FLANNEL_CNI_TAG
 RUN git clone --depth=1 https://github.com/containernetworking/plugins.git $GOPATH/src/github.com/containernetworking/plugins \
     && cd $GOPATH/src/github.com/containernetworking/plugins \
     && git fetch --all --tags --prune \
@@ -16,13 +18,23 @@ RUN git clone --depth=1 https://github.com/containernetworking/plugins.git $GOPA
         -X github.com/containernetworking/plugins/pkg/utils/buildversion.BuildVersion=${TAG} \
         -linkmode=external -extldflags \"-static -Wl,--fatal-warnings\" \
     "
+
+RUN git clone --depth=1 https://github.com/flannel-io/cni-plugin.git $GOPATH/src/github.com/flannel-io/cni-plugin \
+    && cd $GOPATH/src/github.com/flannel-io/cni-plugin \
+    && git fetch --all --tags --prune \
+    && git checkout tags/${FLANNEL_CNI_TAG} -b ${FLANNEL_CNI_TAG} \
+    && go mod vendor \
+    && make build_linux \
+    && install -s dist/flannel-amd64 $GOPATH/src/github.com/containernetworking/plugins/bin/flannel
+
 WORKDIR $GOPATH/src/github.com/containernetworking/plugins
 RUN go-assert-static.sh bin/* \
     && go-assert-boring.sh \
     bin/bandwidth \
     bin/bridge \
     bin/dhcp \
     bin/firewall \
+    bin/flannel \
     bin/host-device \
     bin/host-local \
     bin/ipvlan \