e2e: use bridge cni plugin by default

Bridge networking is stupid and simple and works perfectly in our one
node cluster setup. More complicated CNI setup brings no value in terms
of testing cri-resmgr. Using bridge speeds up tests considerably (by
eliminating all clilium/weavenet download and initialization time) plus
should virtually eliminate all test flakyness related to CNI plugin
failures.

demo/lib/distro.bash

@@ -381,10 +381,6 @@ centos-8-install-containerd-pre() {
     distro-install-repo https://download.docker.com/linux/centos/docker-ce.repo
 }
 
-centos-7-k8s-cni() {
-    echo "weavenet"
-}
-
 centos-install-golang() {
     distro-install-pkg wget tar gzip git-core
     from-tarball-install-golang
@@ -1059,7 +1055,7 @@ default-install-utils() {
 }
 
 default-k8s-cni() {
-    echo ${k8scni:-cilium}
+    echo ${k8scni:-bridge}
 }
 
 default-k8s-cni-subnet() {

demo/lib/vm.bash

@@ -1046,6 +1046,25 @@ vm-destroy-cluster() {
     vm-command "yes | kubeadm reset; rm -f ~$user/.kube/config ~root/.kube/config /etc/kubernetes"
 }
 
+vm-install-cni-bridge() {
+    vm-command "rm -rf /etc/cni/net.d/* && mkdir -p /etc/cni/net.d && cat > /etc/cni/net.d/10-bridge.conf <<EOF
+{
+  \"cniVersion\": \"0.4.0\",
+  \"name\": \"demonet\",
+  \"type\": \"bridge\",
+  \"isGateway\": true,
+  \"ipMasq\": true,
+  \"ipam\": {
+    \"type\": \"host-local\",
+    \"subnet\": \"$CNI_SUBNET\",
+    \"routes\": [
+      { \"dst\": \"0.0.0.0/0\" }
+    ]
+  }
+}
+EOF"
+}
+
 vm-install-cni-cilium() {
     if ! vm-command "curl -L --remote-name-all https://github.com/cilium/cilium-cli/releases/latest/download/cilium-linux-amd64.tar.gz && tar xzvfC cilium-linux-amd64.tar.gz /usr/local/bin && cilium install && rm -f cilium-linux-amd64.tar.gz"; then
         command-error "installing cilium CNI to Kubernetes failed"