TestWeaveTaggerOverlayTopology is flaky

[tomwilkie]

@davkal saw this, now I've just seen it.

--- FAIL: TestWeaveTaggerOverlayTopology (0.00s)
    weave_test.go:69: 
        --- want
        +++ have
        @@ -14,20 +14,13 @@
          Container: (report.Topology) {
           Nodes: (report.Nodes) (len=1) {
            (string) (len=18) "host1;83183a667c01": (report.Node) {
        -    Metadata: (report.Metadata) (len=3) {
        +    Metadata: (report.Metadata) (len=2) {
              (string) (len=19) "docker_container_id": (string) (len=12) "83183a667c01",
        -     (string) (len=18) "weave_dns_hostname": (string) (len=20) "hostname.weave.local",
        -     (string) (len=17) "weave_mac_address": (string) (len=17) "d6:f2:5a:12:36:a8"
        +     (string) (len=18) "weave_dns_hostname": (string) (len=20) "hostname.weave.local"
             },
             Counters: (report.Counters) {
             },
        -    Sets: (report.Sets) (len=2) {
        -     (string) (len=20) "docker_container_ips": (report.StringSet) (len=1 cap=1) {
        -      (string) (len=10) "10.0.0.123"
        -     },
        -     (string) (len=32) "docker_container_ips_with_scopes": (report.StringSet) (len=1 cap=1) {
        -      (string) (len=11) ";10.0.0.123"
        -     }
        +    Sets: (report.Sets) {
             },
             Adjacency: (report.IDList) <nil>,
             Edges: (report.EdgeMetadatas) {

FAIL
FAIL    github.com/weaveworks/scope/probe/overlay   0.066s