Use ensure-tox role from zuul-jobs

We have a role to handle this, lets us it.

Change-Id: I471a852a1d01ef79d7f1408176b72c1db3663a8c
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

playbooks/python-docs/pre.yaml

@@ -3,4 +3,5 @@
     - role: bindep
       bindep_profile: test
       bindep_dir: "src/{{ zuul.project.canonical_name }}"
+    - ensure-tox
     - revoke-sudo

playbooks/python-docs/run.yaml

@@ -1,7 +1,3 @@
 - hosts: all
-  pre_tasks:
-    - name: Ensure tox is installed
-      shell: type tox || pip install --user tox
-
   roles:
     - role: tox

playbooks/python-tarball/pre.yaml

@@ -5,4 +5,5 @@
       bindep_dir: "src/{{ zuul.project.canonical_name }}"
       bindep_command: /usr/bindep-env/bin/bindep
       bindep_fallback: /usr/local/jenkins/common_data/bindep-fallback.txt
+    - ensure-tox
     - revoke-sudo

playbooks/python-tarball/run.yaml

@@ -1,8 +1,4 @@
 - hosts: all
-  pre_tasks:
-    - name: Ensure tox is installed
-      shell: type tox || pip install --user tox
-
   roles:
     - role: tox
       tox_extra_args: -vv python setup.py sdist