Run bindep for proposal jobs

We need gettext on the systems for the translations jobs, this should be
part of the bindep setup. Since we invoke tox, add bindep and tox setup
in pre-run.

Also, some proposal jobs need pyyaml, so add python-yaml to bindep.txt -
and use bindep for all proposal jobs.

Change-Id: I3c0e4741e1c0186b78859841db1ca5c791d4806b

bindep.txt

@@ -2,3 +2,4 @@ language-pack-en [platform:ubuntu]
 libffi-dev [platform:dpkg]
 libffi-devel [platform:rpm]
 libjpeg-dev [platform:dpkg]
+python-yaml [platform:dpkg]

playbooks/proposal/pre.yaml

@@ -6,3 +6,7 @@
   roles:
     - legacy-copy-project-config-scripts
     - add-sshkey
+    - role: bindep
+      bindep_profile: test
+      bindep_dir: "{{ zuul.project.src_dir }}"
+    - ensure-tox