update-report: allow skipping analytics message.

This is used by the install script so it can simplify it's logic and
make the analytics messaging more prominent.

Library/Homebrew/cmd/update-report.rb

@@ -26,7 +26,7 @@ module Homebrew
       analytics_disabled = \
         Utils.popen_read("git", "config", "--local", "--get", "homebrew.analyticsdisabled").chuzzle
       if analytics_message_displayed != "true" && analytics_disabled != "true" &&
-         !ENV["HOMEBREW_NO_ANALYTICS"]
+         !ENV["HOMEBREW_NO_ANALYTICS"] && !ENV["HOMEBREW_NO_ANALYTICS_MESSAGE_OUTPUT"]
         ENV["HOMEBREW_NO_ANALYTICS_THIS_RUN"] = "1"
         # Use the shell's audible bell.
         print "\a"