chore(controller): update PostgreSQL driver to 2.6

See http://initd.org/psycopg/articles/2015/02/09/psycopg-26-and-255-released/

Author: mboersma

controller/requirements.txt

@@ -13,7 +13,7 @@ djangorestframework==3.0.4
 docker-py==0.6.0
 gunicorn==19.2.1
 paramiko==1.15.2
-psycopg2==2.5.4
+psycopg2==2.6
 python-etcd==0.3.2
 PyYAML==3.11
 static==1.1.1