Allow tests to reset bottle hooks on teardown

This avoids polluting other tests that might invoke the installer, thus
executing any registered hooks.

Library/Homebrew/hooks/bottles.rb

@@ -26,6 +26,10 @@ module Homebrew
         return false unless @pour_bottle
         @pour_bottle.call formula
       end
+
+      def self.reset_hooks
+        @has_bottle = @pour_bottle = nil
+      end
     end
   end
 end

Library/Homebrew/test/test_bottle_hooks.rb

@@ -37,4 +37,8 @@ class BottleHookTests < Homebrew::TestCase
     end
     @fi.pour
   end
+
+  def teardown
+    Homebrew::Hooks::Bottles.reset_hooks
+  end
 end