kubelet: use env vars in node log query PS command

- Use environment variables to pass string arguments in the node log
  query PS command
- Split getLoggingCmd into getLoggingCmdEnv and getLoggingCmdArgs
  for better modularization

staging/src/k8s.io/kubelet/config/v1beta1/types.go

@@ -720,6 +720,8 @@ type KubeletConfiguration struct {
 	EnableSystemLogHandler *bool `json:"enableSystemLogHandler,omitempty"`
 	// enableSystemLogQuery enables the node log query feature on the /logs endpoint.
 	// EnableSystemLogHandler has to be enabled in addition for this feature to work.
+	// Enabling this feature has security implications. The recommendation is to enable it on a need basis for debugging
+	// purposes and disabling otherwise.
 	// Default: false
 	// +featureGate=NodeLogQuery
 	// +optional