Install keepalived in neutron_l3_agent container

L3 HA requires keepalived. It has to be installed when install_type
is source.

Change-Id: I3265b74490559ca9b22a19917a76925a55e32cdd
Closes-bug: 1588829

docker/neutron/neutron-l3-agent/Dockerfile.j2

 FROM {{ namespace }}/{{ image_prefix }}neutron-base:{{ tag }}
 MAINTAINER {{ maintainer }}
 
-{% if base_distro in ['ubuntu', 'debian'] %}
-    {% if install_type == 'binary' %}
+{% if install_type == 'binary' %}
+    {% if base_distro in ['ubuntu', 'debian'] %}
 
 RUN apt-get -y install --no-install-recommends \
         neutron-l3-agent \
     && apt-get clean
 
+    {% endif %}
+{% elif install_type == 'source' %}
+    {% if base_distro in ['centos', 'fedora', 'oraclelinux', 'rhel'] %}
+
+RUN yum -y install \
+        keepalived \
+    && yum clean all
+
+    {% elif base_distro in ['ubuntu', 'debian'] %}
+
+RUN apt-get -y install --no-install-recommends \
+        keepalived \
+    && apt-get clean
+
     {% endif %}
 {% endif %}