Add deletion of floating ip after disassociation

First problem - we have 2 very simmilar tests
that differs only by 1 step. In this patch
this 2 tests merge into 1.

Second one - during the tests we do not release
floating ip, we just disassociate it,
and release only in teardown(
when all tests from suite were executed).To fix this issue
add floating ip deleteion as a separate step

Change-Id: I5cc0a782cdc5914e250ae5176aa8a724b797a934
Closes-bug: #1288547