allow to disassociate more than one floating ips

Summary
========
Currently the user able to disassociate one ip at one time.
with this change the user able to disassociate more than one ip at a time.

Description
==========
disassociating a floating ip when there is more than one associated with the instance will disassociate the last one added automatically.
1. it would be nice to be able to select which one you would like to dissociate
2. it would be nice to be able to disassociate all ip's at once

Steps to Reproduce:
1. launch an instance
2. associate more than one floating ip to the instance
3. disassociate the ip

Actual results:

last one added is the last one removed.
if we want to disassociate all ips we need to do it one at a time.

Expected results:

we should be able to disassociate more than one ip at a time
if more than one ip is associated with an instance we should be able to select which one to disassociate.