Add tox max version

So far Tobiko had only a minimum tox version.

But since version 4, tox had some issues with its variables settings.
For example, in Octavia faults workflow - we set tox to run a specific
path and for some reason it is changing when the octavia_faults tox
variable is used.

The same happens with other components sanity tests (it runs the full
sanity suite) etc.

This patch adds a max version to tox, so we won't use version 4 at least
until it will be fixed.

Change-Id: I35d8e5ea2c31afac379585fb6fb9ccbbd2ae4bfc

roles/tobiko-ensure-tox/defaults/main.yaml

@@ -2,3 +2,4 @@
 
 tox_command: tox
 tox_min_version: 3.8
+tox_max_version: 4.0

roles/tobiko-ensure-tox/tasks/tox.yaml

@@ -2,7 +2,7 @@
 
 - name: "ensure Tox is installed"
   command: >
-    {{ python_executable }} -m pip install --user 'tox>={{ tox_min_version }}'
+    {{ python_executable }} -m pip install --user 'tox>={{ tox_min_version }},<{{tox_max_version}}'
   register: install_tox
   changed_when: "'Successfully installed' in install_tox.stdout"