Fix installation of contextlib2

Contextlib2 need to be between 0.5 and 0.6 for queens.
Since upgrade job tries to upgrade from queens to pike, the task were
skipped because the release has change to pike.

Change-Id: Ic692f57c8828e776f49e6c703e50e20d4bc87fe4
Closes-Bug: #1867023

roles/build-test-packages/tasks/main.yml

@@ -44,7 +44,7 @@
 # "'virtualenv' is a package and cannot be directly executed"
 - name: Make sure we have contextlib2 between 0.5 < 0.6 when queens
   become: true
-  when: release in ['queens']
+  when: (release in ['queens']) or (lookup('env', 'ZUUL_BRANCH') | replace('stable/', '') in ['queens'])
   tags: notest
   pip:
     name: contextlib2>0.5.0,<0.6.0