Commit I1d4ded9959c05c65b04b118b1c31b8e6db652e67 rehomed the
availability zone extension's API definition into neutron-lib and
I761381de0d6e26a0380386700e7921b824991669 will consume it in neutron.
This patch switches the relevant code over to use neutron-lib rather
then neutron.
Change-Id: I2145fb4664bfa5c0af8937be6c6932883f278983