Comment 26 for bug 1753209

I personally think the solution of this problem is a lack in base test case classes. When a test case doesn't specify a network to use, it should create one using some parameters specified in tempest.conf. Using a shared network by default (implicitly, without any notice, and without choosing it) makes testing shared networks near to impossible in the contest of running test cases in parallel and therefore should be forbidden and limited to very specific test cases where shared network is explicitly pick up by test case.