test: pid: zone

Add unit-tests for the PID zone module.
Add zone_mock.

Tested: Ran on quanta-q71l board and it behaved as expected.

Change-Id: I51185b2d2daacea6ffb687e8f38c4fe2b2a1bed3
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/pid/thermalcontroller.hpp b/pid/thermalcontroller.hpp
index dbfcfc9..32d4a7f 100644
--- a/pid/thermalcontroller.hpp
+++ b/pid/thermalcontroller.hpp
@@ -16,7 +16,7 @@
 {
     public:
         static std::unique_ptr<PIDController> CreateThermalPid(
-            PIDZone* owner,
+            ZoneInterface* owner,
             const std::string& id,
             std::vector<std::string>& inputs,
             float setpoint,
@@ -24,7 +24,7 @@
 
         ThermalController(const std::string& id,
                           std::vector<std::string>& inputs,
-                          PIDZone* owner)
+                          ZoneInterface* owner)
             : PIDController(id, owner),
               _inputs(inputs)
         { }