On an update, read the snapshots in priority order
On an update, read the snapshots in priority order

When the record is constructed we generate a goroutine to watch each
branch. When any update happens we create one snapshot per branch
and look for the highest-priority value.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

docker/datakit,docker/datakit,docker/datakit