add libpq-dev and python-dev to build psycopg2

This patch adds build prerequisites for psycopg2-2.8.3 as per [1]

[1]: http://initd.org/psycopg/docs/install.html

Change-Id: I591776f5e356152655b9c453644a79b397559f4f

bindep.txt

@@ -0,0 +1,6 @@
+# This is a cross-platform list tracking distribution packages needed for install and tests;
+# see https://docs.openstack.org/infra/bindep/ for additional information.
+
+# libpq-dev is needed by openstack-tox-py37 build only.
+libpq-dev [platform:dpkg test]
+python-dev [platform:dpkg test]

tox.ini

@@ -121,3 +121,15 @@ deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
+
+[testenv:bindep]
+# Do not install any requirements. We want this to be fast and work even if
+# system dependencies are missing, since it's used to tell you what system
+# dependencies are missing! This also means that bindep must be installed
+# separately, outside of the requirements files, and develop mode disabled
+# explicitly to avoid unnecessarily installing the checked-out repo too (this
+# further relies on "tox.skipsdist = True" above).
+basepython = python3
+deps = bindep
+commands = bindep test
+usedevelop = False