Added bindep.txt to the project

This allows to avoid installing unneeded packages when in gate, saving
some time when preparing environment for unit and other non-dsvm tests.

Change-Id: I09aa9c7ebebf12d0c0cce7457fef57f8451fcffa

bindep.txt

@@ -0,0 +1,5 @@
+# This file contains runtime (non-python) dependencies
+# More info at: http://docs.openstack.org/infra/bindep/readme.html
+
+# tools/misc-sanity-checks.sh validates .po[t] files
+gettext [test]

tox.ini

@@ -147,3 +147,13 @@ local-check-factory = neutron.hacking.checks.factory
 
 [testenv:genconfig]
 commands = {toxinidir}/tools/generate_config_file_samples.sh
+
+# 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