Ensure the bandwith plugin chooses the host veth device

When chained with a plugin that returns multiple devices, the bandwidth
plugin chooses the host veth device.

Signed-off-by: Tyler Schultz <tschultz@pivotal.io>

integration/testdata/basic-bridge/network-chain-test.json

@@ -0,0 +1,12 @@
+{
+  "cniVersion": "0.3.1",
+  "name": "network-chain-test",
+  "type": "bridge",
+  "bridge": "test-bridge-0",
+  "isDefaultGateway": true,
+  "ipam": {
+    "type": "host-local",
+    "subnet": "10.11.2.0/24",
+    "dataDir": "/tmp/foo"
+  }
+}