Disable "proxy_request_buffer off" derective for models with trusty

It's necessary to set the "request_buffer" parameter to True to disable
this nginx derective: 

https://gerrit.mcp.mirantis.net/gitweb?p=salt-formulas/nginx.git;a=blob;f=nginx/files/proxy.conf;hb=652f4977b0d949c98de292ad197733c60a028c39#l87

Change-Id: I30e01fda20409b45836f138a591fcfcf38d8d919
Closes-bug: PROD-20481
diff --git a/classes/cluster/virtual-mcp-mitaka-dvr-trusty/openstack/proxy.yml b/classes/cluster/virtual-mcp-mitaka-dvr-trusty/openstack/proxy.yml
index 5175695..d4feb00 100644
--- a/classes/cluster/virtual-mcp-mitaka-dvr-trusty/openstack/proxy.yml
+++ b/classes/cluster/virtual-mcp-mitaka-dvr-trusty/openstack/proxy.yml
@@ -20,3 +20,6 @@
           redirect:
             protocol: https
             host: $host
+        nginx_proxy_openstack_web:
+          proxy:
+            request_buffer: true
diff --git a/classes/cluster/virtual-mcp-mitaka-ovs-trusty/openstack/proxy.yml b/classes/cluster/virtual-mcp-mitaka-ovs-trusty/openstack/proxy.yml
index 761df7c..8a9f9ad 100644
--- a/classes/cluster/virtual-mcp-mitaka-ovs-trusty/openstack/proxy.yml
+++ b/classes/cluster/virtual-mcp-mitaka-ovs-trusty/openstack/proxy.yml
@@ -20,3 +20,6 @@
           redirect:
             protocol: https
             host: $host
+        nginx_proxy_openstack_web:
+          proxy:
+            request_buffer: true