Add redundancy sensor and cleanup

Add fan redundancy sensor and move some class members
into the base class. Asio now protects against setting
the same number twice, allow it now to simplify code.

Change-Id: Idb6b5ff4746da92be62c4756fe442d5a5ed23f4f
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/sensors/include/Thresholds.hpp b/sensors/include/Thresholds.hpp
index 4a07ca2..3f9aa79 100644
--- a/sensors/include/Thresholds.hpp
+++ b/sensors/include/Thresholds.hpp
@@ -48,7 +48,8 @@
                       const thresholds::Threshold &threshold,
                       std::shared_ptr<sdbusplus::asio::connection> &conn);
 
-void checkThresholds(Sensor *sensor);
+// returns false if a critical threshold has been crossed, true otherwise
+bool checkThresholds(Sensor *sensor);
 void assertThresholds(Sensor *sensor, thresholds::Level level,
                       thresholds::Direction direction, bool assert);
 } // namespace thresholds