This way we can have a single file that wraps scenarios,
`gst-validate-1.0` arguments, as well as a configuration.
It changes the name of `description` of scenarios to use `meta`
The goal is to replace tests describes in python with dictionary
to fully self contained `.validatetest` files which look like:
```
meta,
handles-states=true,
ignore-eos=true,
gst-validate-args = {
"videotestsrc pattern=blue ! video/x-raw,format=I420,framerate=1/1 ! timeoverlay ! $(videosink) name=videosink allocation-meta-flags=0",
},
configs = {
"$(validateflow), pad=videosink:sink, buffers-checksum=true, ignored-fields={\"buffers=meta\", }",
}
play
seek, start=0.0, stop=5.0, flags=accurate+flush, rate=1.0
crank-clock, expected-elapsed-time=0.0
crank-clock, repeat=4, expected-elapsed-time=1.0
crank-clock, expected-elapsed-time=1.0
stop, on-message=eos
```
This also adds the notion of global variables which will be useable
in config files too.
And add some documentation about default variables in scenarios
