Force setting pre-vote flag even if it uses default value.

Signed-off-by: Joshua Zhang <[email protected]>

tests/framework/e2e/cluster.go

@@ -571,6 +571,9 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 	}
 
 	defaultValues := values(*embed.NewConfig())
+	// The default pre-vote config in previous versions may not equal to that in current version.
+	// Clear prevote's default value so cluster always add pre-vote flag even if it uses default value.
+	defaultValues["pre-vote"] = ""
 	overrideValues := values(cfg.ServerConfig)
 	for flag, value := range overrideValues {
 		if defaultValue := defaultValues[flag]; value == "" || value == defaultValue {