Add bindep file

We're missing one of these, which means starting from a bare node
it's not completely possible to install openstackclient based only
on bindep and pip. Add one that allows building and installing.

Change-Id: I7b297bb1485773df3d5d1cc3ba78b0b9af4b2d00

Author: emonty

bindep.txt

@@ -0,0 +1,10 @@
+# This is a cross-platform list tracking distribution packages needed by tests;
+# see https://docs.openstack.org/infra/bindep/ for additional information.
+
+gcc [compile test]
+libffi-devel [platform:rpm]
+libffi-dev [compile test platform:dpkg]
+libffi6 [platform:dpkg]
+libssl-dev [compile test platform:dpkg]
+python3-dev [compile test platform:dpkg]
+python3-devel [compile test platform:rpm]