l2 policy creation failure when setting network id

[Yapeng Wu]

When testing Juno code, executing "l2policy-create" command, the CLI returns failure.

The following is the script I used to reproduce the problem.
source openrc admin demo

gbp l3policy-create --description my_l3_policy_1 --ip-version 4 --ip-pool 172.16.0.0/16 --subnet-prefix-length 25 my_l3_policy-1
Created a new l3_policy:
+----------------------+--------------------------------------+
| Field | Value |
+----------------------+--------------------------------------+
| description | my_l3_policy_1 |
| external_segments | {} |
| id | 0ac593b6-8679-43ce-bc73-c2f52410d99f |
| ip_pool | 172.16.0.0/16 |
| ip_version | 4 |
| l2_policies | |
| name | my_l3_policy-1 |
| routers | 6efbd38a-79c1-4543-a60e-f1e35061cb12 |
| shared | False |
| subnet_prefix_length | 25 |
| tenant_id | 063fe8e699894312a2fd52394f9419e8 |
+----------------------+--------------------------------------+

neutron net-create my-net-web-1
Created a new network:
+---------------------------+--------------------------------------+
| Field | Value |
+---------------------------+--------------------------------------+
| admin_state_up | True |
| id | 8447d203-cd6c-45e3-80a4-b08d8adc993d |
| name | my-net-web-1 |
| provider:network_type | vxlan |
| provider:physical_network | |
| provider:segmentation_id | 1001 |
| router:external | False |
| shared | False |
| status | ACTIVE |
| subnets | |
| tenant_id | 063fe8e699894312a2fd52394f9419e8 |
+---------------------------+--------------------------------------+

gbp l2policy-create --description "My L2 Policy Web 1" --network 8447d203-cd6c-45e3-80a4-b08d8adc993d --l3-policy 0ac593b6-8679-43ce-bc73-c2f52410d99f my-l2-policy-web-1
'Client' object has no attribute 'list_networks'