At the moment, we are actually going ahead and sending
an API request for every single member when doing a batch
update, this can be very expensive in large number of
members and will cause a big hit against the Neutron API,
it potentially also makes those API calls timeout.
This patch instead implements a simple cache (per batch
call) to simply store the subnets which are considered valid
which means that it will make significantly less calls,
potentially even one.
It also adjusts the behaviour so that it only runs this on newly
added members which should avoid running it for deleted and
updated members which won't have an effect in this change.
Change-Id: I24ec7dc3b18111c126bcfdaa0780bfd7993020fb
(cherry picked from commit e0a9ba1560)
b8fe15b649