Move OS state interface to state/hostX

Move OS state interface from state/os to state/hostX to make it
consistent with phosphor-state-manager.

Tested result:
```
root@harma:~# busctl introspect xyz.openbmc_project.State.Host0 /xyz/openbmc_project/state/host0 xyz.openbmc_project.State.OperatingSystem.Status
NAME                                             TYPE      SIGNATURE RESULT/VALUE                             FLAGS
.OperatingSystemState                            property  s         "xyz.openbmc_project.State.OperatingSys… emits-change
```

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Change-Id: Idd744285ce3c43add37d17ddd2de4eb6c250853d
diff --git a/src/power_control.cpp b/src/power_control.cpp
index 6aa0314..bba7088 100644
--- a/src/power_control.cpp
+++ b/src/power_control.cpp
@@ -3400,7 +3400,7 @@
 
     // OS State Interface
     osIface = osServer.add_interface(
-        "/xyz/openbmc_project/state/os",
+        "/xyz/openbmc_project/state/host" + node,
         "xyz.openbmc_project.State.OperatingSystem.Status");
 
     // Get the initial OS state based on POST complete