Fix SDF namespacing for Video Plugin

[davetcoleman]

Fixes video plugin for Kinetic, and removes the following warnings with Baxter/other ROS-robots:

ros.gazebo_plugins.video: GazeboRosVideo plugin missing <robotNamespace>, defaults to "".
ros.gazebo_plugins.video: GazeboRosVideo Plugin (ns = ) missing <topicName>, defaults to "image_raw".
ros.gazebo_plugins.video: GazeboRosVideo Plugin (ns = ) missing <height>, defaults to 240.
ros.gazebo_plugins.video: GazeboRosVideo Plugin (ns = ) missing <width>, defaults to 320

This does not fix the related issue reported on bitbucket for the video plugin

This fix initially created and tested by @IanTheEngineer
This PR is sponsored by Vicarious

[davetcoleman]

I've finally figured out why they set this issue as resolved on Bitbucket - the warnings go away if you switch to the OSRF debians and the latest 7.5.0 version of Gazebo instead of the Ubuntu universe 7.0.0 version.

Still, this PR is backwards compatible and provides support for both 7.0 and 7.5, so I think it should be merged.

[piyushk]

I can confirm that this works as expected, and allows setting plugin parameters again.

Thanks @davetcoleman!

[IanTheEngineer]

+1 Thanks for taking the time to apply the patch Dave.

[j-rivero]

I can confirm that this works as expected, and allows setting plugin parameters again.

If we have a confirmation, @davetcoleman feel free to merge. Thanks guys.

[davetcoleman]

Thanks @IanTheEngineer for initially creating this fix!