Add python-cinderclient to requirements.txt

The scenario tests manager has an import for cinderclient, however
python-cinderclient was not listed as a requirement. This corrects
the oversight by adding python-cinderclient to requirements.txt.

Change-Id: I92cc4144cc2392391ee80a4f55783acd0f70c483
diff --git a/requirements.txt b/requirements.txt
index 4873d75..19d6e0b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -12,6 +12,7 @@
 python-keystoneclient>=0.2.0
 python-novaclient>=2.10.0
 python-quantumclient>=2.1
+python-cinderclient>=1.0.4,<2
 testresources
 keyring
 testrepository