test: fix veth test failing when another veth exists
test: fix veth test failing when another veth exists

Change-Id: I804c0654ef142b7d6652d30be4b4343ed79ba905

safchain/skydive,safchain/skydive,lebauce/skydive,lebauce/skydive,redhat-cip/skydive,safchain/skydive,lebauce/skydive,safchain/skydive,skydive-project/skydive,safchain/skydive,lebauce/skydive,skydive-project/skydive,skydive-project/skydive,skydive-project/skydive,skydive-project/skydive,safchain/skydive,redhat-cip/skydive,redhat-cip/skydive,lebauce/skydive,lebauce/skydive,lebauce/skydive,safchain/skydive,safchain/skydive,skydive-project/skydive,lebauce/skydive,skydive-project/skydive