call new obmc-chassis-blackout@.target on blackout

The following commit introduced a new systemd target to be called when
OpenBMC firmware detects a power blackout has occurred (system
unexpectedly lost all power to system):
  https://gerrit.openbmc.org/c/openbmc/docs/+/54204

This target is now in place and the appropriate services have been
installed into it. Switch the state-manager code over to call this new
target.

Tested:
    - Verified in simulation that the target was called when the system
      experienced a blackout.

From a powered off state.
root@p10bmc: systemctl stop xyz.openbmc_project.State.Chassis.service

Manipulated file to indicate that the power was on before service ended
root@p10bmc: vi /var/lib/chassStateChangeTime

root@p10bmc: systemctl start xyz.openbmc_project.State.Chassis.service
Jun 22 17:05:37 p10bmc phosphor-chassis-state-manager[1155]:
            The system suffered a power blackout.

root@p10bmc: systemctl status obmc-chassis-blackout@0.target
            Active: active since Wed 2022-06-22 17:05:37 UTC; 8s ago

root@p10bmc: systemctl status phosphor-reset-state-sensors@0.service
Jun 22 17:05:37 p10bmc systemd[1]: Finished Reset host sensors.

root@p10bmc: systemctl status obmc-led-group-stop@power_on.service
Active: active (exited) since Wed 2022-06-22 17:05:37 UTC; 8s ago

Signed-off-by: Corey Hardesty <corey.hardesty@icloud.com>
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: If95f8da52ec024e699204f4b26784c7457da5abf
diff --git a/chassis_state_manager.cpp b/chassis_state_manager.cpp
index 9bfdb95..ba30c73 100644
--- a/chassis_state_manager.cpp
+++ b/chassis_state_manager.cpp
@@ -44,8 +44,7 @@
 constexpr auto CHASSIS_STATE_HARD_POWEROFF_TGT_FMT =
     "obmc-chassis-hard-poweroff@{}.target";
 constexpr auto CHASSIS_STATE_POWERON_TGT_FMT = "obmc-chassis-poweron@{}.target";
-constexpr auto RESET_HOST_SENSORS_SVC_FMT =
-    "phosphor-reset-sensor-states@{}.service";
+constexpr auto CHASSIS_BLACKOUT_TGT_FMT = "obmc-chassis-blackout@{}.target";
 constexpr auto AUTO_POWER_RESTORE_SVC_FMT =
     "phosphor-discover-system-state@{}.service";
 constexpr auto ACTIVE_STATE = "active";
@@ -155,9 +154,8 @@
                         "Chassis power was on before the BMC reboot and it is off now");
 
                     // Reset host sensors since system is off now
-                    // TODO: when CHASSIS_BLACKOUT_TGT will include this service
-                    // Needs to be removed when the blackout target is merged
-                    startUnit(fmt::format(RESET_HOST_SENSORS_SVC_FMT, id));
+                    // Ensure Power Leds are off.
+                    startUnit(fmt::format(CHASSIS_BLACKOUT_TGT_FMT, id));
 
                     setStateChangeTime();
                     // Generate file indicating AC loss occurred