Fix cleanup of default security group when preprov creds are used

Patch [1] fixes cleanup of default security group for
tempest.api.network.admin.test_negative_quotas.* tests but also
introduces a bug [2] that makes the tests fail when preprovisioned
credentials are used.

This patch reverts some changes from patch [1] and tries to
fix the cleanup of default security group in a way that works
also for preprovisioned credentials.

[1] https://review.opendev.org/c/openstack/tempest/+/797466/7
[2] https://bugs.launchpad.net/tempest/+bug/1939049

Closes-Bug: 1939049
Change-Id: I00a9cc48866e41c3c559628de5af4ba017beba39
3 files changed