regulators: Add detectPhaseFaults() to Chassis

Add a detectPhaseFaults() method to the Chassis class.  This method
detects redundant phase faults in all regulator devices in the chassis.

Add a gtest test case to exercise the new code.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: Ie4efce27e4c96c2f77831434c94e07dcd5c3d7db
diff --git a/phosphor-regulators/src/chassis.cpp b/phosphor-regulators/src/chassis.cpp
index 425c20e..a8c8ed6 100644
--- a/phosphor-regulators/src/chassis.cpp
+++ b/phosphor-regulators/src/chassis.cpp
@@ -74,6 +74,15 @@
     }
 }
 
+void Chassis::detectPhaseFaults(Services& services, System& system)
+{
+    // Detect phase faults in each device
+    for (std::unique_ptr<Device>& device : devices)
+    {
+        device->detectPhaseFaults(services, system, *this);
+    }
+}
+
 void Chassis::monitorSensors(Services& services, System& system)
 {
     // Monitor sensors in each device