Add debug mode

Description:
    1. Could enable debug mode by adding file: /etc/thermal.d/debugging.
        $ mkdir /etc/thermal.d
        $ touch /etc/thermal.d/debugging
        $ systemctl restart phosphor-pid-control

    2. Could record fans output PWM, chosen temperature, PID/stepwise output PWM in debug mode.

Design:
    1. Create debugging file and restart service to enable debug mode.

    2. Check if debug mode is enabled to output fans output PWM, chosen temperature,
       PID/stepwise output PWM, and so on.

Test Case:
    1. Enable debug mode and check logs: pass

Change-Id: I8527ebcb81e723298ba7e786b4501f986ebd439e
Signed-off-by: Bonnie Lo <Bonnie_Lo@wiwynn.com>
diff --git a/pid/zone.hpp b/pid/zone.hpp
index 41514a7..0504a6d 100644
--- a/pid/zone.hpp
+++ b/pid/zone.hpp
@@ -60,7 +60,7 @@
     void setManualMode(bool mode);
     bool getFailSafeMode(void) const override;
 
-    int64_t getZoneID(void) const;
+    int64_t getZoneID(void) const override;
     void addSetPoint(double setPoint, const std::string& name) override;
     double getMaxSetPointRequest(void) const override;
     void addRPMCeiling(double ceiling) override;