Taking roi in cameraInfo in consideration when using camera_display plugin

[Shin-nn]

This should fix camera_display when using roi.

[dhood]

This looks good, thanks for the patch.

Thinking about behaviour stability: this will change the behaviour for users with cameras with ROI set, but given that those users currently have the subimage stretched to the full camera width, I think this will be a welcome improvement for those users.

There's a chance this will negatively impact the following user: ROI set in the camera info, but image being published at full size. This previously would have rendered the image appropriately but now will distort the image according to the ROI. However, the camera info ought to match the camera image, so this user shouldn't exist, so I do not consider this a reason to prevent this change.

@wjwwood if you have a chance to confirm that this behavioural change is appropriate to push into kinetic that would be appreciated.

camera display with roi (selected in red) without this patch (top right, stretched)

camera display with roi (selected in red) with this patch (top right, not stretched, appropriate size)

The images are from testing with turtlebot in gazebo and interactive ROI selection; launch/config file: camera_roi.zip

[dhood]

@wjwwood I've requested your review, not to hurry it up, just so it's less likely to get lost over the holidays

[dhood]

@wjwwood I'm planning to push the behaviour fix into kinetic FYI