[demo] Camera images via lossy wifi about ros2

[esteve]

Add QoS options to publisher/subscriber APIs

[wjwwood]

Multiple streams with different QoS, should stress network.
Multiple OS in the demo.

[BobDean]

what resolution images and at what Hz are you targeting? My default question for people is "How will you handle a 25MPixel stereo pair"?

This NIST link may help track down a network simujlator: http://www-x.antd.nist.gov/nistnet/

[wjwwood]

We were going to start with something more reasonable, like 1280x1024 at 30 hz. I don't think it's realistic to do 25Mp stereo pair over crowded wifi, but we can work up to it in our testing. The 25Mp pair might be a valid test for the intraprocess image pipeline, but that really depends on the computer you're running it on.

NIST net looks like an interesting lead on network simulation. Thanks @BobDean.

[gerkey]

We now have a test setup working, publishing images from camera to a camera viewer node.

Next up is tweaking QoS settings, and if necessary, messing with network interface behavior via tc.

Write a single-host tutorial that shows how to see the effect over localhost. Might need to disable shared memory transport somehow.

[dirk-thomas]

Shipped.