XACRO Support

[tobiasduerschmid]

In order to find bug fixes like this one, we should be able to analyze .xacro files like this one:

<xacro:if value="$(arg imu_enabled)">
    <gazebo>
      <plugin name="imu_controller" filename="libhector_gazebo_ros_imu.so">
        <robotNamespace>/</robotNamespace>
        <updateRate>50.0</updateRate> 
        <bodyName>base_link</bodyName>
        <topicName>imu/data_compass</topicName>
        <accelDrift>0.005 0.005 0.005</accelDrift>
        <accelGaussianNoise>0.005 0.005 0.005</accelGaussianNoise>
        <rateDrift>0.005 0.005 0.005 </rateDrift>
        <rateGaussianNoise>0.005 0.005 0.005 </rateGaussianNoise>
        <headingDrift>0.005</headingDrift>
        <headingGaussianNoise>0.005</headingGaussianNoise>
      </plugin>
    </gazebo>
  </xacro:if>

The full file can be found here.