Implement pool session persistence in the NSX-v3 driver.
This patch does also a certain amount of refactoring to ensure
still a single call is made for updating the NSX virtual server.
Persitence profile deletion happens via a deferred function as
the virtual server must be updated first to not use anymore
the persistence profile.
Updating a pool from cookie-based to source-ip based session
persistence is currently not allowed and will result in a driver
error.
Change-Id: Id9fc4e664c5a212a411b4d4eda688bad5c74e869
2e010fd9b2