Upgrade packages when installing openstack-clients

This resolves the package versions conflicts we saw recently and fixes
source image building gate.

Change-Id: I489499e447ac1b7bb82ae9d69eb5b7fe7bd7591d
Closes-Bug: #1498303

docker/openstack-base/Dockerfile.j2

@@ -23,7 +23,7 @@ RUN apt-get install -y --no-install-recommends \
 RUN curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py \
     && python get-pip.py \
     && rm get-pip.py \
-    && pip --no-cache-dir install \
+    && pip --no-cache-dir install -U \
         python-barbicanclient \
         python-ceilometerclient \
         python-congressclient \