appc/cni#76 added a "dns" field in the result JSON. But before this
patch, the plugins had no way of knowing which name server to return.
There could be two ways of knowing which name server to return:
1. add it as an extra argument ("CNI_ARGS")
2. add it in the network configuration as a convenience (received via
stdin)
I chose the second way because it is easier. In the case of rkt, it
means the user could just add the DNS name servers in
/etc/rkt/net.d/mynetwork.conf.
In some cases the route deletion would fail due to wrong
scope. It should be NOWHERE when deleting (per iproute2).
This also adds more verbose error messages.
Instead of allocating a /31 for each container,
use the same IP on the host side for all veths.
This is very similar how real point-to-point
devices work (using donor IPs).
This takes some of the machinery from CNI and from the rkt networking
code, and turns it into a library that can be linked into go apps.
Included is an example command-line application that uses the library,
called `cnitool`.
Other headline changes:
* Plugin exec'ing is factored out
The motivation here is to factor out the protocol for invoking
plugins. To that end, a generalisation of the code from api.go and
pkg/plugin/ipam.go goes into pkg/invoke/exec.go.
* Move argument-handling and conf-loading into public API
The fact that the arguments get turned into an environment for the
plugin is incidental to the API; so, provide a way of supplying them
as a struct or saying "just use the same arguments as I got" (the
latter is for IPAM plugins).
