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
2 files changed