Because:
- They are not necessary.
- Neutron agent scheduler code (reschedule_resources_from_down_agents)
seems to (correctly) assume each get_admin_context() call returns
a fresh context. This mocking breaks it.
- Right now, Neutron agentdb uses the new engine facade [1] and
Neutron agent scheduler doesn't. It causes caching issue in our
unit tests. (See the Related-Bug) Stopping reusing contexts
(thus sessions) would prevent the issue.
[1] https://review.openstack.org/#/c/611462/
Related-Bug: #1803745
Change-Id: Ia986f98f8bda9c7cde33af3dfdf2e45a2685fd6d
7f82a19155