issue #543: install virtualenv for Azure

.ci/localhost_ansible_tests.py

@@ -23,7 +23,7 @@ with ci_lib.Fold('unit_tests'):
 
 with ci_lib.Fold('job_setup'):
     # Don't set -U as that will upgrade Paramiko to a non-2.6 compatible version.
-    run("pip install -q ansible==%s", ci_lib.ANSIBLE_VERSION)
+    run("pip install -q virtualenv ansible==%s", ci_lib.ANSIBLE_VERSION)
 
     os.chmod(KEY_PATH, int('0600', 8))
     if not ci_lib.exists_in_path('sshpass'):