Rename tox_venvlist (1/2)

For consistency with the tox jobs, use tox_envlist instead of
tox_venvlist.

We need first to add a new parameter, then change the job, then
remove the old parameter.

Change-Id: Id03d4c1351d5a002dc9d73247d0315bef274f627
Needed-By: I67a20b1faa77ff0166ad96fd95432c11948abc74

.zuul.yaml

@@ -80,6 +80,7 @@
         tempest: True
       tempest_test_regex: '^neutron_tempest_plugin\.scenario\.test_dns_integration'
       tox_venvlist: all-plugin
+      tox_envlist: all-plugin
     irrelevant-files:
       - ^(test-|)requirements.txt$
       - ^releasenotes/.*$