- Closes#150, #394.
- Introduces `AttachmentConfiguration` type so that we can add key-value
options to `--network` in the future.
- Eliminates redundant `ContainersService.Item` type.
- Since we now ensure at ContainersService that hostnames will not
conflict, the network helper IP allocator now simply provides the
existing IP if for an allocation on an existing hostname, which should
handle (in an eventually consistent way) the case where a container
fails to deallocate an IP on shutdown.
- Part of #384.
- Rename to reflect that these are not just client defaults.
- Relocate so callers don't need the heavyweight coupling to
ContainerClient to access the type.
J Logan