Rally tests configure public/shared networks - should be private

Rally tests create shared=true/public networks that are confusing and potentially harmful to cloud user operations.

Rally testing should not affect user-facing network/project availability as it can affect user interface and process.

Imagine having only one network when using horizon to spin up an instance would allow you to not visit the network tab, but having two choices in networks due to an errant public/shared rally network will cause user to have to use the network tab to specify which network to connect new instances to.

Here's an example rally network from the charm:

# openstack network show b8e62d31-727e-4d5b-8e47-b31b1a9e8d97
+---------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| Field | Value |
+---------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | |
| availability_zones | nova |
| created_at | 2020-03-28T17:45:13Z |
| description | |
| dns_domain | |
| id | b8e62d31-727e-4d5b-8e47-b31b1a9e8d97 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| is_default | None |
| is_vlan_transparent | None |
| location | cloud='', project.domain_id=, project.domain_name=, project.id='bc2d95bfe1a4469ab9b6e6fe16fab71b', project.name=, region_name='DCS1', zone= |
| mtu | 8950 |
| name | rally_verify_53ba7ff6_WZppbOTR |
| port_security_enabled | True |
| project_id | bc2d95bfe1a4469ab9b6e6fe16fab71b |
| provider:network_type | vxlan |
| provider:physical_network | None |
| provider:segmentation_id | 1052 |
| qos_policy_id | None |
| revision_number | 3 |
| router:external | Internal |
| segments | None |
| shared | True |
| status | ACTIVE |
| subnets | d07b0438-e155-4e11-9313-e043b51067bf |
| tags | |
| updated_at | 2020-03-28T17:45:19Z |
+---------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+

Please update rally network creation to set shared=False.