Install ebtables in neutron-linuxbridge

Otherwise it complains about missing the ebtables binary.

Change-Id: I6bc0c0b1bacdf4a75929424ad9f11f6982e62c87
Closes-bug: #1473500

docker/centos/binary/neutron/neutron-linuxbridge-agent/Dockerfile

@@ -2,7 +2,7 @@ FROM %%KOLLA_NAMESPACE%%/%%KOLLA_PREFIX%%neutron-base:%%KOLLA_TAG%%
 MAINTAINER Kolla Project (https://launchpad.net/kolla)
 
 # Install required packages
-RUN yum install -y openstack-neutron-linuxbridge && \
+RUN yum install -y ebtables openstack-neutron-linuxbridge && \
     yum clean all
 
 COPY check.sh start.sh /