obmc-initfs: run update as a sub-script

The update script has replicated logic to do the final reboot, kexec,
halt, or poweroff command.  Instead of transferring control via exec
just call it as a normal command, and return to shutdown for the
final mounted fs debug print and command.

Signed-off-by: Milton Miller <miltonm@us.ibm.com>
diff --git a/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-shutdown.sh b/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-shutdown.sh
index d530265..7d1157a 100644
--- a/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-shutdown.sh
+++ b/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-shutdown.sh
@@ -34,7 +34,7 @@
 
 if test -x /update && ls $image* > /dev/null 2>&1
 then
-	exec /update ${1+"$@"}
+	/update ${1+"$@"}
 fi
 
 echo Remaining mounts:
@@ -43,7 +43,6 @@
 test "umount_proc" && umount /proc && rmdir /proc
 
 
-
 # Execute the command systemd told us to ...
 if test -d /oldroot  && test "$1"
 then