Add integration tests

[joaoantoniocardoso]

First step towards #378

How to test locally

1. Install v4l2loopback:

• Ubuntu: sudo apt-get install -y v4l2loopback-dkms
• Arch: sudo pacman -S v4l2loopback-dkms v4l2loopback-utils

2. Add a v4l2loopback device:

sudo modprobe v4l2loopback video_nr=42 && \
sudo v4l2loopback-ctl delete /dev/video42 && \
sudo v4l2loopback-ctl add --exclusive-caps 0 --max-openers 2 --name potato --verbose /dev/video42

3. Get qrtimestamp plugins:

wget -q https://github.com/patrickelectric/qrtimestamp-gst/releases/download/0.1.0/libgstqrtimestamp-x86_64.so.tar -O - | tar -x
export GST_PLUGIN_PATH="$PWD:$GST_PLUGIN_PATH"

4. Run the test

cargo test --release --locked --test v4l2_latency_and_jitter

5. Clean up

sudo modprobe -r v4l2loopback