Merge pull request #48237 from xiangpengzhao/fix-proxy-test

Automatic merge from submit-queue

Add test for kube-proxy running with "--cleanup-iptables=true"

**What this PR does / why we need it**:
Add test to prevent such kube-proxy panic to happen again.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #48177

**Special notes for your reviewer**:
Forgot to add this in last PR #48183. Should we also add this to v1.7 milestone?
/cc @ncdc @dchen1107 

**Release note**:

```release-note
NONE
```

cmd/kube-proxy/app/server_test.go

@@ -195,6 +195,7 @@ func TestProxyServerWithCleanupAndExit(t *testing.T) {
 		assert.Nil(t, err, "unexpected error in NewProxyServer, addr: %s", addr)
 		assert.NotNil(t, proxyserver, "nil proxy server obj, addr: %s", addr)
 		assert.NotNil(t, proxyserver.IptInterface, "nil iptables intf, addr: %s", addr)
+		assert.True(t, proxyserver.CleanupAndExit, "false CleanupAndExit, addr: %s", addr)
 
 		// Clean up config for next test case
 		configz.Delete("componentconfig")