Any container definitions in ccl.toml can be given a `start_order` tag
(integer). It is recommended to not put a start_order unless a container
depends on another one (e.g. synapse needs postgres), in which case all
dependents and dependees should be given a `start_order`, with dependees
having a lower number than their dependents. It is guaranteed that the
dependees will be started first, although the container startup
procedure is outside of our control. Containers without a `start_order`
will have their operations applied asynchronously, but those with
a start order are started, well, in order from lowest to highest. "Stop"
operations are applied in the reverse order.
Large change greatly expanding the linked footprint of this little
utility, but it is much faster and adds a couple of very nice features:
- set container sysctl settings to disable router advertisements as part
of container definition. this means we no longer need to do this via
`ip netns exec <container> sysctl -w ...` (followed by
`ip netns exec ip -6 a flush...`). Major win.
- able to very quickly ascertain creation and run state of defined
containers.
