Support multi vehicle sitl gazebo without ros

Tools/gazebo_sitl_multiple_run.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+# run multiple instances of the 'px4' binary, but w/o starting the simulator.
+# It assumes px4 is already built, with 'make px4_sitl_default'
+
+# The simulator is expected to send to TCP port 4560+i for i in [0, N-1]
+# For example jmavsim can be run like this:
+#./Tools/jmavsim_run.sh -p 4561 -l
+
+sitl_num=2
+[ -n "$1" ] && sitl_num="$1"
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+src_path="$SCRIPT_DIR/.."
+
+build_path=${src_path}/build/px4_sitl_default
+mavlink_udp_port=14560
+mavlink_tcp_port=4560
+world="empty"
+
+echo "killing running instances"
+pkill -x px4 || true
+
+sleep 1
+
+export PX4_SIM_MODEL=iris
+
+echo "Starting gazebo"
+gzserver ${src_path}/Tools/sitl_gazebo/worlds/${world}.world --verbose &
+sleep 5
+
+n=0
+while [ $n -lt $sitl_num ]; do
+	working_dir="$build_path/instance_$n"
+	[ ! -d "$working_dir" ] && mkdir -p "$working_dir"
+
+	pushd "$working_dir" &>/dev/null
+	echo "starting instance $n in $(pwd)"
+	../bin/px4 -i $n -d "$src_path/ROMFS/px4fmu_common" -w sitl_iris_${n} -s etc/init.d-posix/rcS >out.log 2>err.log &
+	xacro ${src_path}/Tools/sitl_gazebo/models/rotors_description/urdf/iris_base.xacro rotors_description_dir:=${src_path}/Tools/sitl_gazebo/models/rotors_description mavlink_udp_port:=$((14560+$n)) mavlink_tcp_port:=$((4560+$n)) --inorder > /tmp/${PX4_SIM_MODEL}_${n}.urdf
+	echo "Spawning ${PX4_SIM_MODEL}_${n}"
+	gz model --spawn-file=/tmp/${PX4_SIM_MODEL}_${n}.urdf --model-name=${PX4_SIM_MODEL}_${n} -x 0.0 -y ${n} -z 0.0
+
+	popd &>/dev/null
+
+	n=$(($n + 1))
+done
+
+echo "Starting gazebo client"
+gzclient