sensors: change object_manager path

As per PDI, all sensor implementation shall put object manager at
`/xyz/openbmc_project/sensors`.
[1] https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml#L20

Tested: on hardware, ipmitool sdr elist is working.
```
CPU              | 36h | ok  |  0.1 |
CPU_Kernel       | 37h | ok  |  0.1 |
CPU_User         | 38h | ok  |  0.1 |
Memory_Available | 39h | ok  |  0.1 |
Storage_RW       | 3Ah | ok  |  0.1 |
```

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Ia9b21eebf37cb22cfa4bc19f2369423ea4d5c035
diff --git a/healthMonitor.hpp b/healthMonitor.hpp
index bba3b52..c6e77dd 100644
--- a/healthMonitor.hpp
+++ b/healthMonitor.hpp
@@ -2,6 +2,7 @@
 #include <phosphor-logging/lg2.hpp>
 #include <sdbusplus/bus.hpp>
 #include <sdbusplus/message.hpp>
+#include <sdbusplus/server/manager.hpp>
 #include <sdeventplus/clock.hpp>
 #include <sdeventplus/event.hpp>
 #include <sdeventplus/utility/timer.hpp>
@@ -162,7 +163,8 @@
      *
      * @param[in] bus     - Handle to system dbus
      */
-    HealthMon(sdbusplus::bus_t& bus) : bus(bus)
+    HealthMon(sdbusplus::bus_t& bus) :
+        bus(bus), sensorsObjectManager(bus, "/xyz/openbmc_project/sensors")
     {
         // Read JSON file
         sensorConfigs = getHealthConfig();
@@ -193,6 +195,7 @@
     sdbusplus::bus_t& bus;
     std::vector<HealthConfig> sensorConfigs;
     std::vector<HealthConfig> getHealthConfig();
+    sdbusplus::server::manager_t sensorsObjectManager;
 };
 
 } // namespace health