Add bindep.txt file

Bindep is a tool for checking the presence of binary packages needed
to use an application / library. It started life as a way to make it
easier to set up a development environment for OpenStack projects.

Change-Id: I28dd0e00734be85cb4b66a09708c0dee8dcb5ef1
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

bindep.txt

@@ -0,0 +1,4 @@
+# This is a cross-platform list tracking distribution packages needed by tests;
+# see http://docs.openstack.org/infra/bindep/ for additional information.
+
+graphviz [doc test]

tox.ini

@@ -184,3 +184,13 @@ deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
+
+# This environment can be used to quickly validate that all needed system
+# packages required to successfully execute test targets are installed
+[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.
+deps = bindep
+commands = bindep test