bindep: use virtualenv_command from ensure-pip

This role currently assumes virtualenv is installed when installing
bindep; instead run ensure-pip to both ensure the pip package
requirements are there, and use the abstracted virtualenv command it
provides.

Change-Id: I4dbd7d23fe770c07dc333dd8579d4f8978410a95

roles/bindep/tasks/install.yaml

@@ -6,10 +6,15 @@
   notify:
     - remove bindep temp dir
 
+- name: Ensure we have pip dependencies
+  include_role:
+    name: ensure-pip
+
 - name: install bindep into temporary venv
   pip:
     name: bindep
-    virtualenv: "{{ bindep_temp_dir.path }}/venv"
+    virtualenv_command: '{{ ensure_pip_virtualenv_command }}'
+    virtualenv: '{{ bindep_temp_dir.path }}/venv'
 
 - name: Define bindep_command
   set_fact: