[fwaas]Disassociate all ports before deleting firewall group

If the firewall group has associated ports, the firewall group may be in
an active state. Firewall group is active, deletion is not allowed.
This patch cannot solve the bug[1] at the moment. Because there are
other bugs[2] present.
We plan to avoid bugs[2] through patches[3] now. To solve the bug[1].
There are other patches[1] here to try and solve the bug[2].

Partial-Bug: #2018967

[1] https://bugs.launchpad.net/neutron/+bug/2018967
[2] https://bugs.launchpad.net/neutron/+bug/2021457
[3] https://review.opendev.org/c/openstack/neutron-fwaas/+/884333
[4] https://review.opendev.org/c/openstack/neutron-fwaas/+/884335

Change-Id: Id328446be8591fac3affe2cf8adeaeee09697085
1 file changed