Unified interface for ScenarioTest and NetworkScenarioTest

Allows scenarios to use similar methods for Floating IP and network checks
regardless of network implementation done by Nova/Neutron

Creates floating IP helpers for Nova clients

Moves connectivity check helpers to manager.ScenarioTest to be used with both
classes

Change-Id: Id6a9feb7bcab811a5b5d4985397c419c02b4269a
Merge "Unified interface for ScenarioTest and NetworkScenarioTest"