kubelet: add CNI cache dir option and plumb through to CNI and kubenet

libcni 0.7.0 caches ADD operation results and allows the runtime to
retrieve these from the cache. In case the user wants a different
cache directory than the defaul, plumb that through like we do
for --cni-bin-dir and --cni-conf-dir.

cmd/kubelet/app/options/container_runtime.go

@@ -54,7 +54,8 @@ func NewContainerRuntimeOptions() *config.ContainerRuntimeOptions {
 		ExperimentalDockershim:     false,
 
 		//Alpha feature
-		CNIBinDir:  "/opt/cni/bin",
-		CNIConfDir: "/etc/cni/net.d",
+		CNIBinDir:   "/opt/cni/bin",
+		CNIConfDir:  "/etc/cni/net.d",
+		CNICacheDir: "/var/lib/cni/cache",
 	}
 }

cmd/kubelet/app/server.go

@@ -1251,6 +1251,7 @@ func RunDockershim(f *options.KubeletFlags, c *kubeletconfiginternal.KubeletConf
 		PluginName:         r.NetworkPluginName,
 		PluginConfDir:      r.CNIConfDir,
 		PluginBinDirString: r.CNIBinDir,
+		PluginCacheDir:     r.CNICacheDir,
 		MTU:                int(r.NetworkPluginMTU),
 	}