Add Path=/ explicitly to vcap session cookie

Without this the default is the path of the current request
so if user visits /foo/bar and then /bar he will get different
cookies, and if sticky sessions are in effect those requests
will land on different servers in the back end.

Change-Id: I009b74d33c77d5fb854006cc91582aa159aafcbd

ext/nginx/uls.lua

@@ -168,7 +168,7 @@ function vcap_handle_cookies(ngx)
   end
   if not sticky then return end
 
-  local vcap_cookie = VCAP_SESSION_ID.."="..ngx.var.sticky
+  local vcap_cookie = VCAP_SESSION_ID.."="..ngx.var.sticky.."; Path=/"
 
   ngx.log(ngx.DEBUG, "generate cookie:"..vcap_cookie.." for resp from:"..
           ngx.var.backend_addr)