priority.session is meant to be used to set routing priorities.
priority.driver is meant to be used by the scheduler to select what
nodes is best for driving the graph. This usually depends on the
hardware quality and the use case (Pro Audio devices are likely
to be used as driving the graph).
See #1028
Don't just store the id in the metadata but a JSON object with
the node name. This makes it possible to easily introspect the
metadata and also extend the metadata with more fields later.
Instead of matching the metadata id to the global ids we now
have to match it against the name.
Check if the properties got update before we try to parse them.
If they are not updated, they might be empty and we would lose
our previously parse values.
Fixes default volume in alsa-mixer.
