added iproute2 package (cni plugin execs nsenter ... ip)

Dockerfile

@@ -1,9 +1,11 @@
 FROM debian:buster-slim
 
 # > cni.go:364] [...] exec: "iptables": executable file not found in $PATH
+# > docker_sandbox.go:394] failed to read pod IP from plugin/docker: networkPlugin cni [...]: unexpected command output nsenter: failed to execute ip: No such file or directory
 RUN apt-get update && apt-get install --yes --no-install-recommends \
     ca-certificates \
     curl \
+    iproute2 \
     iptables
 
 ARG KUBERNETES_VERSION=v1.17.0