[S-RBAC] Fix tests for port RBAC policies

Exisitng tests didn't mock "get_network" function properly thus
there was no "network:tenant_id" field in the target object set and
OwnerCheck check was failing for the "net_owner".
Unit tests were green because they badly expected e.g. for the
ProjectMember that e.g. port with given fixed_ip or mac_address will not
be allowed (exception was raised because net_owner check failed) even
thoug it should be possible through the net_owner rule in policy.

This patch fixes mocking get_network function in unit tests module for
the port RBAC policies and it also updates unit tests accordingly to
make them pass.

Change-Id: I4c26403e237afdb8934dda65fef3b12c99a5f689
Signed-off-by: Slawek Kaplonski <[email protected]>
(cherry picked from commit a48b715)

Author: slawqo