Fix test_network_quota_exceeding test

This patch makes sure that the test cleans up properly
default security group which gets created with the
new project from the setUp function.

Before, the test deleted only project and left the
security group unremoved.

The reason why the project is created in setUp function
is explained in [1][2].

[1] https://github.com/openstack/tempest/commit/e094bbade2b719fd531c2c8a7284ebfb1fb32efc
[2] https://bugs.launchpad.net/tempest/+bug/1789938

Change-Id: Ie7381ee1a90fa8e075ca246c065eaec3c92e1092
Closes-Bug: 1925132
Co-authored-by: Aleksey Myltsev
2 files changed