Added a test launch file and a default configuration file for the MPU9250 IMU.

config/mpu9250_imu_sim_config.yaml

+rate: 100.0
+namespace: '/imu'
+tf_prefix: '/mpu9250'
+imu_topic: 'imu'
+accel_offset_x: 0.06
+accel_offset_y: 0.06
+accel_offset_z: 0.08
+accel_drift_x: 0.001
+accel_drift_y: 0.001
+accel_drift_z: 0.001
+accel_noise_x: 0.008
+accel_noise_y: 0.008
+accel_noise_z: 0.008
+rate_offset_x: 5.0
+rate_offset_y: 5.0
+rate_offset_z: 5.0
+rate_drift_x: 0.015
+rate_drift_y: 0.015
+rate_drift_z: 0.015
+rate_noise_x: 0.1
+rate_noise_y: 0.1
+rate_noise_z: 0.1
+heading_offset: 0.0
+heading_drift: 0.0
+heading_noise: 0.0
+

launch/mpu9250_imu_sim.launch

+<?xml version="1.0" encoding="UTF-8"?>
+<launch>
+
+  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
+  <include file="$(find gazebo_ros)/launch/empty_world.launch">
+    <arg name="paused" value="false"/>
+    <arg name="use_sim_time" value="true"/>
+    <arg name="extra_gazebo_args" value=""/>
+    <arg name="gui" value="true"/>
+    <arg name="recording" value="false"/>
+    <arg name="headless" value="false"/>
+    <arg name="debug" value="false"/>
+    <arg name="physics" value="ode"/>
+    <arg name="verbose" value="false"/>
+    <arg name="world_name" value="worlds/empty.world"/> 
+    <arg name="respawn_gazebo" value="false"/>
+    <arg name="use_clock_frequency" value="false"/>
+    <arg name="pub_clock_frequency" value="100"/>
+  </include>
+
+  <group ns="imu">
+    <param name="robot_description"
+           command="$(find xacro)/xacro --inorder '$(find iri_mpu9250_imu_description)/urdf/mpu9250_imu_example.xacro'" />
+
+    <node pkg="robot_state_publisher" type="state_publisher" name="mpu9250_tf_broadcaster">
+      <param name="tf_prefix" type="string" value="/mpu9250"/>
+      <param name="publish_frequency" type="double" value="20.0"/>
+    </node>
+  
+    <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-param robot_description -urdf -model imu -x 0 -y 0 -z 0 -R 0 -P 0 -Y 0" />
+  </group>
+
+</launch>
+