Remove use of mapper call

Replace invocations of mapper call with a call to busctl and mapper
get-service.  This provides equivalent functionality but opens the
door for dropping a systemd patch we have carried for some time.

Change-Id: Iea0cce89341939b49b095d1f5010415578331d4d
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-stop@.service b/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-stop@.service
index 1321c21..40dbf36 100644
--- a/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-stop@.service
+++ b/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-stop@.service
@@ -10,8 +10,8 @@
 
 [Service]
 RemainAfterExit=yes
-ExecStart=/usr/bin/env mapper call /org/openbmc/control/power%i org.openbmc.control.Power setPowerState i 0
-SyslogIdentifier=mapper
+ExecStart=/bin/sh -c "busctl call `mapper get-service /org/openbmc/control/power%i` /org/openbmc/control/power%i org.openbmc.control.Power setPowerState i 0"
+SyslogIdentifier=op-power-stop
 
 [Install]
 WantedBy=obmc-host-stop@%i.target