Fixes Dockerfile for neutron-lbaas-agent

Remove the extra '\' after RUN command for ubuntu, otherwise the later
COPY will not run correctly for ubuntu image.

Change-Id: Ie7de201711c6e684f58665027888c34f4c245487
Closes-bug: #1605453

docker/neutron/neutron-lbaas-agent/Dockerfile.j2

@@ -28,7 +28,7 @@ RUN apt-get -y install --no-install-recommends \
         neutron-lbaas-common \
         neutron-lbaasv2-agent \
         python-neutron-lbaas \
-    && apt-get clean \
+    && apt-get clean
 
     {% endif %}