[wmf debug] resourceloader: Output servedBy when load.php has an error

Similar to wfReportTime() at the bottom of HTML responses (OutputPage).

Creates output like:

  /*
  Problematic modules: {"meh.not.here":"missing"}
  */
  /*
  Served by: krinkle-mw002.localnet
  */

Bug: 65424
Change-Id: I718fcf23d5eb4fb4b9b3d089f44c4c0f89ea786f