Allocating a pseudo-TTY (-t, --tty) fails when 'run' is executed
inside of a Jenkins or cron script. This change fixes
ttcn3-bts-test, which invokes 'run' to fetch the config files.
Change-Id: If22f682be4f004c5bb43e65098079a4f4fe6158d
Fixes: If15461240f3037c142c176fc7da745a1701ae3f8
Using a separate container will allow us to do gbproxy specific things
like waiting for physical net-devices to show up in the docker netns
before actually starting the osmo-gbproxy executable
Change-Id: I5e6351055ac9430f13e43291cf2a9d52683fe6bf