networking: Add flags to specify net config and net plugin binary dirs.

[yifan-gu]

Add --net-config for net config dir.
Add --net-plugin for net plugin binary dir.

Also did minor refactoring that groups networking related flags together.

cc @iaguis @alban @jonboulle

[yifan-gu]

So for the tests, I am trying to copy some plugin binary to a random directory, change its name, and use --net-plugin to point to that directory, to see if rkt can find the binary as expected.

So where should I copy the plugin binary from? ctx.rktBin()/../tools/macvlan ? @krnowak

[yifan-gu]

@krnowak Could you think of any better way to locate the plugin binary?

[krnowak]

@yifan-gu: My idea was to split stage0 and stage1 config as per #2013. So, stage1 config could allow user to specify net plugins paths and CNI config (in a bit different, but consistent format). This, together with passing user config to stage1 should fix your issue too.

I'm not fond of the --net-config flag - my aim was to actually have net plugins config to be in the same format as other config we have (with rktKind and rktVersion fields). I was working on this several weeks ago, but it started to burn me out, so I switched to something else. Of course, this might not be enough for you, if you wanted to have this quickly.

[krnowak]

For the record - my work is here - https://github.com/kinvolk/rkt/tree/krnowak/config-split-backward-compatible

[yifan-gu]

For the record - my work is here - https://github.com/kinvolk/rkt/tree/krnowak/config-split-backward-compatible

So are we going to get that in for 1.2 or next release? @krnowak

[krnowak]

@yifan-gu: For the next one.

[krnowak]

Here is the preliminary PR that implements the feature - #2312

[jonboulle]

Should this be closed in favour of #2312?

[krnowak]

Yes.