haproxy: Use -f configdir instead of for and xargs

-f configdir has been supported in HaProxy since 1.7

Partial-Bug: #2048130
Change-Id: Icb95cb072cb3eb5c27ffd79a127069bfcf21a61a

ansible/roles/loadbalancer/templates/haproxy/haproxy_run.sh.j2

@@ -35,6 +35,4 @@ fi
 {% endif %}
 {% endif %}
 
-find /etc/haproxy/services.d/ -mindepth 1 -print0 | \
-    xargs -0 -Icfg echo -f cfg | \
-    xargs /usr/sbin/haproxy -W -db -p /run/haproxy.pid -f /etc/haproxy/haproxy.cfg
+exec /usr/sbin/haproxy -W -db -p /run/haproxy.pid -f /etc/haproxy/haproxy.cfg -f /etc/haproxy/services.d/