Make cinder build from source

Either the reference wasn't copied properly, or it changed recently
with Ryan's work.

Change-Id: I2b55affe35104c6baab8804e5452fc7a49bae170
Partially-Implements: blueprint gate-source-builds

docker_templates/cinder/cinder-base/Dockerfile.j2

@@ -25,7 +25,6 @@ RUN cd /cinder \
     && pip install /cinder \
     && mkdir /etc/cinder /var/log/cinder \
     && cp -r /cinder/etc/cinder/* /etc/cinder/ \
-    && cp /etc/cinder/cinder.conf.sample /etc/cinder/cinder.conf \
     && chown -R cinder: /etc/cinder /var/log/cinder \
     && rm -rf /root/.cache