diamond: add diamond::collector::nginx resource

* Update nginx submodule for I9450b8cf0.
* See <https://github.com/BrightcoveOS/Diamond/wiki/collectors-NginxCollector>
  for details.
* Provision a collector for the rcstream Nginxes.

Change-Id: I79611947724ba6dc424c1267128687abd30c10bb
Merge "diamond: add diamond::collector::nginx resource" into production