config: add tests for a couple documented configs

[euank]

These tests additions were prompted by issue #3916.

Ideally all documented configs would be included here (possibly via living outside of the docs and having the copy in the docs be templated in or such).

[euank]

Semaphore appears to be flaking on a networking issue unrelated to this pr:

Output: "gc: moving pod \"94616432-4eb6-4fed-a406-0be0e936125c\" to garbage
Garbage collecting pod \"94616432-4eb6-4fed-a406-0be0e936125c\"
stage0: Execing [/tmp/datadir-967761143/pods/exited-garbage/94616432-4eb6-4fed-a406-0be0e936125c/stage1/rootfs/gc --debug --local-config /tmp/localdir-160387050 94616432-4eb6-4fed-a406-0be0e936125c]
stage1 gc: Removing journal link.
stage1 gc: Cleaning up cgroups.
stage1 gc: Tearing down networks.
networking: error on removing masquerading
  └─exit status 1: iptables: No chain/target/match by that name.
"

Sounds like an nftables kernel module is missing?

[lucab]

@euank is that a single flake or does it persist across retries?

[euank]

I've seen it twice in a row now. I don't have permissions on the rkt semaphore to poke around too much though.

[lucab]

@euank it looks like you were missing from the semaphore team, added you now.