Change how HMAC bulk_copy params are sent to Metis

[coleshaw]

Currently, we do something like

    client.send(
      'body_request',
      Net::HTTP::Post,
      hmac.url_params[:path] + '?' + hmac.url_params[:query],
      bulk_copy_params)

But we should consider changing that to:

    hmac_params_hash = Hash[cgi_string.map {|key,values| [key.to_sym, values[0]||true]}]
    client.send(
        'body_request',
        Net::HTTP::Post,
        hmac.url_params[:path],
        params.merge(hmac_params_hash))

because with a lot of revisions, we get a Metis-side error:

 "-//IETF//DTD HTML 2.0//EN"> (Etna::Error)
<html><head>
<title>414 Request-URI Too Long</title>
</head><body>
<h1>Request-URI Too Long</h1>
<p>The requested URL's length exceeds the capacity
limit for this server.<br />
</p>
</body></html>

This is because the Etna::Hmac library puts a copy of all the extra headers passed in into hmac.url_params[:query] into new values, like X-Etna-Revisions ... which gets long.