Allow selecting balance method for mysql, pgsql and horizon types

Change-Id: I546ff87f34b3c4352009237fe5ff91009357cd6e
diff --git a/haproxy/files/haproxy.cfg b/haproxy/files/haproxy.cfg
index 7aae743..5926ace 100644
--- a/haproxy/files/haproxy.cfg
+++ b/haproxy/files/haproxy.cfg
@@ -76,7 +76,7 @@
   timeout client 300s
   timeout server 300s
   {%- elif listen.get('type', None) == 'mysql' %}
-  balance leastconn
+  balance {{ listen.get('balance', 'leastconn') }}
   mode tcp
   option httpchk
   option tcplog
@@ -86,7 +86,7 @@
   timeout server  300s
   option mysql-check user haproxy
   {%- elif listen.get('type', None) == 'pgsql' %}
-  balance leastconn
+  balance {{ listen.get('balance', 'leastconn') }}
   mode tcp
   option httpchk
   option tcplog
@@ -96,7 +96,7 @@
   timeout server  28801s
   option pgsql-check user postgres
   {%- elif listen.get('type', None) == 'horizon' %}
-  balance  source
+  balance {{ listen.get('balance', 'source') }}
   capture  cookie vgnvisitor= len 32
   cookie  SERVERID insert indirect nocache
   mode http