Verified that this issue is no longer seen. 

Browbeat+Rally was run with times set to 500, concurrency set to 16 and rerun set to 3. After the completion of the run, all the networks/routers created by rally are deleted in neutron DB as well as ODl datastore. The only networks/routers that remain are the ones I manually created before kicking off browbeat. No extra networks/routers are seen.

(overcloud) [stack@c08-h21-r630 ansible]$ openstack network list
+--------------------------------------+---------+--------------------------------------+
| ID                                   | Name    | Subnets                              |
+--------------------------------------+---------+--------------------------------------+
| 234f117e-64d6-4beb-8f9d-c38ecb94bd89 | private | 2e7e585a-67de-4687-8e7e-36aa6723316e |
| af377378-fd27-43ae-a2a8-844907bdf713 | public  | 06dcd089-4518-44e4-96eb-4173402c0484 |
+--------------------------------------+---------+--------------------------------------+

[root@overcloud-controller-0 heat-admin]# curl -s -u admin:YANBwTyEKhEdKXyebDNvcgWHQ -X GET http://172.16.0.19:8081/restconf/config/neutron:neutron/networks | python -m json.tool
{
    "networks": {
        "network": [
            {
                "admin-state-up": true,
                "name": "private",
                "neutron-L3-ext:external": false,
                "neutron-provider-ext:network-type": "neutron-networks:network-type-vxlan",
                "neutron-provider-ext:segmentation-id": "30",
                "project-id": "b174a20ee67a4abeb22b52b4a368afd2",
                "revision-number": 2,
                "shared": false,
                "status": "ACTIVE",
                "tenant-id": "b174a20e-e67a-4abe-b22b-52b4a368afd2",
                "uuid": "234f117e-64d6-4beb-8f9d-c38ecb94bd89"
            },
            {
                "admin-state-up": false,
                "name": "Sync Canary Network",
                "neutron-L3-ext:external": false,
                "neutron-provider-ext:network-type": "neutron-networks:network-type-flat",
                "project-id": "bd8db3a8-2b30-4083-a8b3-b3fd46401142",
                "shared": false,
                "status": "ACTIVE",
                "tenant-id": "bd8db3a8-2b30-4083-a8b3-b3fd46401142",
                "uuid": "bd8db3a8-2b30-4083-a8b3-b3fd46401142"
            },
            {
                "admin-state-up": true,
                "name": "public",
                "neutron-L3-ext:external": true,
                "neutron-provider-ext:network-type": "neutron-networks:network-type-vlan",
                "neutron-provider-ext:physical-network": "datacentre",
                "neutron-provider-ext:segmentation-id": "10",
                "revision-number": 5,
                "shared": true,
                "status": "ACTIVE",
                "uuid": "af377378-fd27-43ae-a2a8-844907bdf713"
            }
        ]
    }
}

ODl container iamge: 2018-11-05.3
RPM: opendaylight-8.3.0-7.el7ost.noarch

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2019:0093