Create tox_environment_defaults variable for tox based jobs

Expose the ability for tox jobs to define a default set of
environmental variables to pass to the tox role.  We also do a few new
things.

Check to see if tox_environment and tox_environment_defaults are
defined, if so combined tox_environment_defaults with
tox_environment creating a new my_tox_environment variable.
Variables defined in tox_environment take priority when we combine
variables.

Change-Id: Ic4a5644e79ca7000cbdaee40467619a6832c8332
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

roles/tox/defaults/main.yaml

@@ -1,3 +1,5 @@
 ---
 tox_envlist: venv
 zuul_work_dir: "src/{{ zuul.project.canonical_name }}"
+tox_environment: {}
+tox_environment_defaults: {}

roles/tox/tasks/main.yaml

@@ -3,11 +3,15 @@
     msg: "tox_envlist is required for this role"
   when: tox_envlist is not defined
 
+- name: Create my_tox_environment variable
+  set_fact:
+    my_tox_environment: "{{ tox_environment_defaults | combine(tox_environment) }}"
+
 - name: Run tox
   args:
     chdir: "{{ zuul_work_dir }}"
     executable: /bin/bash
-  environment: "{{ tox_environment | default(omit) }}"
+  environment: "{{ my_tox_environment }}"
   shell: |
     # If a bundle file is present, call tox with the jenkins version of
     # the test environment so it is used.  Otherwise, use the normal

zuul.yaml

@@ -44,19 +44,24 @@
       This performs basic host and general project setup tasks common
       to all tox unit test jobs.
 
-      Responds to three variables:
+      Responds to these variables:
 
       tox_envlist
         work against specified environments (ALL selects all)
 
       tox_environment
-        list of environmental variables to pass to bash shell
+        list of user defined environmental variables to pass to bash shell
 
       tox_command_line
         an optional command line
     run: playbooks/tox/run
     pre-run: playbooks/tox/pre
     post-run: playbooks/tox/post
+    vars:
+      tox_environment_defaults:
+        NOSE_WITH_HTML_OUTPUT: 1
+        NOSE_HTML_OUT_FILE: nose_results.html
+        NOSE_WITH_XUNIT: 1
 
 - job:
     name: tox-py27