When project_id/tenant_id is present in an API call, Neutron
checks first if this project exists. If not, a HTTPNotFound
will be thrown.
This patch is tested in neutron-tempest-plugin:
https://review.opendev.org/#/c/754390/
Closes-Bug: #1896588
Change-Id: I6276490d4df69ec0f2c9a1492b9b03d1130c7c05