Fix get_dev in namespaced environments
Fix get_dev in namespaced environments

Commit cd9ab2911952ac42 fixed device selection in environments that have
multiple devices, but unfortunately broke it on apt.postgresql.org,
where the tests are running in network namespaces via veth/ceth devices.
This fixes the detection to support both.

cybertec-postgresql/vip-manager,cybertec-postgresql/vip-manager