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-start@.service b/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-start@.service
index dc3174d..c1de92f 100644
--- a/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-start@.service
+++ b/common/recipes-phosphor/chassis/obmc-op-control-power/op-power-start@.service
@@ -12,8 +12,8 @@
 [Service]
 RemainAfterExit=yes
 Type=oneshot
-ExecStart=/usr/bin/env mapper call /org/openbmc/control/power%i org.openbmc.control.Power setPowerState i 1
-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 1"
+SyslogIdentifier=op-power-start
 
 [Install]
 WantedBy=obmc-host-start@%i.target