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/fans/obmc-control-fan/obmc-max-fans.service b/common/recipes-phosphor/fans/obmc-control-fan/obmc-max-fans.service
index c426c44..f062fc9 100644
--- a/common/recipes-phosphor/fans/obmc-control-fan/obmc-max-fans.service
+++ b/common/recipes-phosphor/fans/obmc-control-fan/obmc-max-fans.service
@@ -7,5 +7,5 @@
 [Service]
 Type=oneshot
 Restart=no
-ExecStart=/usr/bin/env mapper call /org/openbmc/control/fans org.openbmc.control.Fans setMax
-SyslogIdentifier=mapper
+ExecStart=/bin/sh -c "busctl call `mapper get-service /org/openbmc/control/fans` /org/openbmc/control/fans org.openbmc.control.Fans setMax"
+SyslogIdentifier=obmc-max-fans