scheduled-host-transition: make backward compatible

Similar to what was done with the host and chassis code, ensure the old
d-bus service name, xyz.openbmc_project.State.ScheduledHostTransition,
is registered when the host instance is 0.

This ensures any code or tools that had hard coded the service name
prior to the instance based support continue to work

Tested:
- Confirmed with this change that both
  xyz.openbmc_project.State.ScheduledHostTransition and
  xyz.openbmc_project.State.ScheduledHostTransition0 work

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I1fb5ca622db01c931d70461d0ab4847c890b6df7
diff --git a/scheduled_host_transition_main.cpp b/scheduled_host_transition_main.cpp
index 7e02f8d..0962bda 100644
--- a/scheduled_host_transition_main.cpp
+++ b/scheduled_host_transition_main.cpp
@@ -56,6 +56,13 @@
     phosphor::state::manager::ScheduledHostTransition manager(
         bus, objPathInst.c_str(), hostId, event);
 
+    // For backwards compatibility, request a busname without host id if
+    // input id is 0.
+    if (hostId == 0)
+    {
+        bus.request_name(SCHEDULED_HOST_TRANSITION_BUSNAME);
+    }
+
     bus.request_name((std::string{SCHEDULED_HOST_TRANSITION_BUSNAME} +
                       std::to_string(hostId))
                          .c_str());