FIX: Reopen sidekiq log files after rotation (#9429)

Unicorn uses the USR1 to indicate that log files should be reopened. This commit implements the same functionality for our forked sidekiq workers:

- USR1 is intercepted in the unicorn master, and re-issued to all child processes
- USR1 is trapped in the sidekiq processes, and `Unicorn::Util.reopen_logs` is used to re-open log files

lib/demon/base.rb

@@ -37,6 +37,13 @@ class Demon::Base
     end
   end
 
+  def self.kill(signal)
+    return unless @demons
+    @demons.values.each do |demon|
+      demon.kill(signal)
+    end
+  end
+
   attr_reader :pid, :parent_pid, :started, :index
   attr_accessor :stop_timeout
 
@@ -63,6 +70,10 @@ class Demon::Base
     end
   end
 
+  def kill(signal)
+    Process.kill(signal, @pid)
+  end
+
   def stop_signal
     "HUP"
   end