Deletes floating ip related connection states

When a floating ip is dissociated with a port, the current
connection with the floating ip is still working. This patch
will clear the connection state and cut off the connection
immediately.

Since conntrack -D will return 1, which is not an error code,
so add extra_ok_codes argument to execute methods.

Change-Id: Ia9bd7ae243a0859dcb97e2fa939f7d16f9c2456c
Closes-Bug: #1334926
(cherry picked from commit 966645538395079b5337b5ed30d597112279283c)
Merge "Deletes floating ip related connection states" into stable/icehouse
Merge branch 'stable/icehouse' of https://github.com/openstack/quantum into stable/icehouse