Change httpcheck method to GET for openstack

According to API documentation OPTIONS method is not supported by API
services. Haproxy perform checks with OPTIONS by default, this patch
switches httpchk by using GET.

Change-Id: Ieb7c9ab75c0b3885d7148f5af1866ef8628cc100
diff --git a/haproxy/files/haproxy.cfg b/haproxy/files/haproxy.cfg
index 34be63c..e423291 100644
--- a/haproxy/files/haproxy.cfg
+++ b/haproxy/files/haproxy.cfg
@@ -130,7 +130,9 @@
   balance {{ listen.get('balance', 'roundrobin') }}
   option  httplog
   {%- elif listen.get('type', None) == 'openstack-service' %}
-  option  httpchk
+  # NOTE(vsaienko): by default haproxy uses OPTIONS method when doing check
+  # This is not guaranteed by openstack APIs, change it to GET instead
+  option  httpchk GET /
   option  httplog
   option  httpclose
   {%- elif listen.get('type', None) == 'heat' %}