hnbgw: add CN pool tests

docker-playground.git needs a config file change to be committed at the
same time as this patch, see 'Related'.

Depends: osmo-ttcn3-hacks I94aa0b2adfc48b98cb4b1efe595c2432fc603d6c
Change-Id: I027a059faed3f140f8801f84338956cd004043b5
7 files changed