Add python-memcache package openstack base

Adding python-memcache package to openstack-base ubuntu docker images.

Closes-Bug: #1577422

Change-Id: I5112c0ba3234a0b3cfc7677f9fbb7c152ab64917

docker/openstack-base/Dockerfile.j2

@@ -167,6 +167,7 @@ RUN apt-get install -y --no-install-recommends \
         python-ironicclient \
         python-magnumclient \
         python-manilaclient \
+        python-memcache \
         python-mistralclient \
         python-muranoclient \
         python-pip \