added tests to improve the code coverage in file ngx_http_lua_headers_out.c.
added tests to improve the code coverage in file ngx_http_lua_headers_out.c.

yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx