Make elasticsearch-specific tests from wagtailimages / wagtaildocs run under tox

tox.ini

@@ -9,7 +9,7 @@ envlist = py{27,33,34,35}-dj{18,19}-{sqlite,postgres,mysql}-{elasticsearch,noela
 [testenv]
 install_command = pip install -e ".[testing]" -U {opts} {packages}
 commands =
-    elasticsearch: coverage run runtests.py wagtail.wagtailsearch --elasticsearch
+    elasticsearch: coverage run runtests.py wagtail.wagtailsearch wagtail.wagtaildocs wagtail.wagtailimages --elasticsearch
     noelasticsearch: coverage run runtests.py
 
 basepython =