Drop environments for nose

... because stestr is now used instead of nose.

Also drop the VIRTUAL_ENV environment which is now automatically set
by tox.

Change-Id: Ied6e20f5b1dc5de384f29d317bec998e86f26efa

Author: kajinamit

tox.ini

@@ -33,12 +33,8 @@ setenv =
 commands = oslo_debug_helper -t kolla/tests {posargs}
 
 [testenv:cover]
-setenv = VIRTUAL_ENV={envdir}
-         NOSE_WITH_COVERAGE=1
-         NOSE_COVER_BRANCHES=1
-         NOSE_COVER_HTML=1
-         NOSE_COVER_HTML_DIR={toxinidir}/cover
-         PYTHON=coverage run --source kolla --parallel-mode
+setenv =
+    PYTHON=coverage run --source kolla --parallel-mode
 commands =
     stestr run {posargs}
     coverage combine