Add delete not found unit testcase for floating_ip api

This patch adds unit test case for the delete api of
floating_ip extension.
V2 and V21 have difference return code when delete
a invalid when given a invalid id of floating ip.

This patch addes both nova-network api and neutronv2 api
test cases.

Partially implements blueprint v2-on-v3-api
Change-Id: I40a5b133c98e01e8f5c613b765b8d821beec03a6
Merge "Add delete not found unit testcase for floating_ip api"