test-bpf: skip test when run inside containers

test-bpf: skip test when run inside containers

The test reliably fails inside LXC and Docker when run on a new enough
kernel. It's unclear whether this is a kernel, LXC/Docker or systemd
issue and apparently there is no real interest to get this fixed, so
let's skip this test.
As this also covers Travis CI, there is no need for this additional
check anymore.

See https://github.com/systemd/systemd/issues/9666

(cherry picked from commit 98a3c188a1511caae422b2c891f3cc016824eb81)

Gbp-Pq: Name test-bpf-skip-test-when-run-inside-containers.patch