Add bindep.txt file to neutron-fwaas repo
Add bindep.txt file to neutron-fwaas repo

It is needed to put there libpq-dev package which is required
at least in py37 job.

Change-Id: I53c5abd7c60c6925cc9dc9ee95a210fcc7e98a6c
Closes-Bug: #1834298

openstack/neutron-fwaas,openstack/neutron-fwaas