merge px4_sitl_ign into px4_sitl_default (#20188)

- for convenience merge px4_sitl_ign into px4_sitl_default, but allow simulator_ignition_bridge to quietly skip inclusion if ignition-transport isn't available
 - simulator_ignition_bridge only try setting the system clock in
lockstep builds
 - this simplifies usage and CI system dependencies

ROMFS/px4fmu_common/init.d-posix/px4-rc.simulator

@@ -33,11 +33,11 @@ elif [ "$PX4_SIMULATOR" = "ignition" ]; then
 		# starting ign gazebo with ${PX4_SIM_WORLD} world
 		echo "INFO  [init] starting ign gazebo"
 
+		ign gazebo --verbose=1 -r -s "${PX4_IGN_GAZEBO_WORLDS}/${PX4_SIM_WORLD}.sdf" &
+
 		if [ -z $HEADLESS ]; then
-			ign gazebo --verbose=1 -r "${PX4_IGN_GAZEBO_WORLDS}/${PX4_SIM_WORLD}.sdf" &
-		else
-			# starting ign gazebo headless
-			ign gazebo --verbose=1 -r -s "${PX4_IGN_GAZEBO_WORLDS}/${PX4_SIM_WORLD}.sdf" &
+			# HEADLESS not set, starting ign gazebo gui
+			ign gazebo -g &
 		fi
 	else
 		echo "INFO  [init] ign gazebo already running world: $ign_world"

ROMFS/px4fmu_common/init.d-posix/rcS

@@ -1,6 +1,9 @@
 #!/bin/sh
 
-set -e
+# Un comment and use set +e to ignore and set -e to enable 'exit on error control'
+set +e
+# Un comment the line below to help debug scripts by printing a trace of the script commands
+#set -x
 
 # PX4 commands need the 'px4-' prefix in bash.
 # (px4-alias.sh is expected to be in the PATH)
@@ -66,7 +69,7 @@ set PARAM_BACKUP_FILE parameters_backup.bson
 
 param select $PARAM_FILE
 if [ -f $PARAM_FILE ]; then
-	set +e # disable exit on error control for param import
+
 	if ! param import
 	then
 		echo "ERROR [init] param import failed"
@@ -92,7 +95,6 @@ if [ -f $PARAM_FILE ]; then
 
 		param status
 	fi
-	set -e # restore exit on error control
 
 elif [ -f $PARAM_BACKUP_FILE ]; then
 	echo "ERROR [init] primary param file $PARAM_FILE unavailable, using backup $PARAM_BACKUP_FILE"