don't swallow error

Since sometimes the error is different from what we expect.

weave

@@ -212,8 +212,8 @@ connect_container_to_bridge() {
 }
 
 launch() {
-    if ! ip netns exec $NETNS ip link show eth0 >/dev/null 2>&1 ; then
-        echo "No eth0 interface inside $CONTAINER_NAME container; perhaps you are running the docker daemon with container networking disabled (-b=none)." >&2
+    if ! ip netns exec $NETNS ip link show eth0 >/dev/null ; then
+        echo "Perhaps you are running the docker daemon with container networking disabled (-b=none)." >&2
         return 1
     fi
     connect_container_to_bridge &&