1. What is the problem
User cannot correctly delete floating ip via the Tricirce plugin.
2. What is the solution to the problem
Overwrite delete_floatingip method in the Tricircle plugin. We
first update the floating ip to disassociate it with fixed ip,
then invoke delete_floatingip method in the base class to delete
the database record.
3. What the features need to be implemented to the Tricircle
to realize the solution
Deletion of floating ip is now supported.
Change-Id: Ia8bf6e7499321c1be085533e8695eea6ac8ef26d