Added tempest_black_regex to skip tempest tests

* https://review.openstack.org/547106 adds a black_regex flag to
  tempest run. We can use the same in devstack-tempest base job
  to skip/blacklist tests.

Change-Id: I9ed91b01ddb7ec0a3d23305031afbac7c4b16c55

roles/run-tempest/README.rst

@@ -39,3 +39,20 @@ Run Tempest
    :default: smoke
 
    The Tempest tox environment to run.
+
+.. zuul:rolevar:: tempest_black_regex
+   :default: ''
+
+   A regular expression used to skip the tests.
+
+   It works only when used with some specific tox environments
+   ('all', 'all-plugin'.)
+
+   Multi-line and commented regexs can be achieved by doing this:
+
+       ::
+           vars:
+             tempest_black_regex: |
+               (?x)    # Ignore comments and whitespaces
+               # Line with only a comment.
+               (tempest.api.identity).*$

roles/run-tempest/defaults/main.yaml

@@ -1,3 +1,4 @@
 devstack_base_dir: /opt/stack
 tempest_test_regex: ''
 tox_envlist: smoke
+tempest_black_regex: ''

roles/run-tempest/tasks/main.yaml

@@ -35,7 +35,9 @@
       when: blacklist_stat.stat.exists
 
 - name: Run Tempest
-  command: tox -e {{tox_envlist}} -- {{tempest_test_regex|quote}} {{blacklist_option|default('')}} --concurrency={{tempest_concurrency|default(default_concurrency)}}
+  command: tox -e {{tox_envlist}} -- {{tempest_test_regex|quote}} {{blacklist_option|default('')}} \
+            --concurrency={{tempest_concurrency|default(default_concurrency)}} \
+            --black-regex={{tempest_black_regex|quote}}
   args:
     chdir: "{{devstack_base_dir}}/tempest"
   become: true