Use cached 'tox_executable' in fetch-tox-output

Otherwise this role could fail when tox is not installed in PATH.

Also updates the default behaviour to only collect the environments
configured with 'envlist' in tox.ini and collects all environments if
the envlist is set to 'ALL'.

Change-Id: I60bcc25cb853d2db3ee767a719b9ac54e421532e

roles/fetch-tox-output/tasks/main.yaml

@@ -25,17 +25,24 @@
     envlist: "{{ tox_envlist.split(',') }}"
   when: tox_envlist is defined
 
-- name: Find all environments
-  command: tox -l
+- name: Find all default environments
+  command: "{{ tox_executable }} -l"
   args:
     chdir: "{{ zuul_work_dir }}"
   register: tox_environments
-  when: tox_envlist is not defined or tox_envlist|lower == 'all'
+  when: tox_envlist is not defined
+
+- name: Find all default environments
+  command: "{{ tox_executable }} -a"
+  args:
+    chdir: "{{ zuul_work_dir }}"
+  register: tox_environments
+  when: tox_envlist == 'ALL'
 
 - name: Set envlist fact
   set_fact:
     envlist: "{{ tox_environments.stdout_lines }}"
-  when: tox_envlist is not defined or tox_envlist|lower == 'all'
+  when: tox_envlist is not defined or tox_envlist == 'ALL'
 
 - name: Copy tox logs
   copy:

test-playbooks/python/fetch-tox-output.yaml

@@ -35,6 +35,8 @@
   tasks:
     - import_role:
         name: fetch-tox-output
+      vars:
+        tox_envlist: "ALL"
 
     - block:
         - name: Undo the log_path fact set by fetch-javascript-output

test-playbooks/tox/reinstall-tox.yaml

@@ -0,0 +1,17 @@
+- hosts: all
+  name: Remove any pre-installed tox
+  tasks:
+    - name: Remove tox package with pip
+      shell: pip uninstall -y tox
+      become: true
+      failed_when: false
+    - name: Remove tox package with pip3
+      shell: pip3 uninstall -y tox
+      become: true
+      failed_when: false
+    - name: Verify tox is not installed
+      command: "tox --version"
+      register: result
+      failed_when: result.rc == 0
+  roles:
+    - ensure-tox

zuul-tests.d/python-jobs.yaml

@@ -250,6 +250,10 @@
       - roles/ensure-output-dirs/.*
       - roles/fetch-tox-output/.*
       - roles/fetch-output/.*
+      - roles/ensure-tox/.*
+      - test-playbooks/python/fetch-tox-output.yaml
+      - test-playbooks/tox/reinstall-tox.yaml
+    pre-run: test-playbooks/tox/reinstall-tox.yaml
     run: test-playbooks/python/fetch-tox-output.yaml
     vars:
       zuul_use_fetch_output: true