ttcn3-bts-test: add env var to not run all configs
Make it possible to e.g. run only one of the generic/oml/hopping configurations.
I made a version of this patch a few weeks ago for testing OS#6375, and I'm submitting it now so I can add multiple configurations for ttcn3-ggsn-test in the next patch with the same logic.
The kernel ttcn3-ggsn-tests have been failing since the osmo-ggsn config for kernel-gtp has been adjusted for v4v6 instead of v4 only.
This new configuration caused a regression with: * linux kernel without Pablo's GTP IPv6 patches * latest stable release of osmo-ggsn, which does not support IPv6
As the kernel patches aren't merged yet, this caused all tests to fail.
Avoid this by running the ttcn3-ggsn-test with multiple configurations: * v4_only: one APN with v4 * v6_only: one APN with v6 * v4v6_only: one APN with v4v6 * all: multiple APNs with all of the above
With this change, the tests running in the v4_only configuration will pass again with the stable versions of osmo-ggsn, libgtpnl and kernel. And with new versions, most test in the other configurations will pass too.
As discussed with Harald, this does not only split up the configuration for osmo-ggsn with kernel gtp-u, but also with the userspace implementation. The "all" config currently only works with the userspace gtp implementation (OS#6106).
