use global ids for message reply to addresses fixes #7723

test plan:
 * send someone a message on another shard
 * reply to that message
 * it should be added to the conversation

Change-Id: Id4439bd63f8805660d302a04e54bd47f304e29b2
Reviewed-on: https://gerrit.instructure.com/9545
Tested-by: Hudson <hudson@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>

app/models/message.rb

@@ -309,7 +309,7 @@ class Message < ActiveRecord::Base
   end
 
   def reply_to_secure_id
-    Canvas::Security.hmac_sha1(self.id.to_s)
+    Canvas::Security.hmac_sha1(self.global_id.to_s)
   end
 
   def reply_to_address
@@ -318,7 +318,7 @@ class Message < ActiveRecord::Base
     res = self.from if self.context_type == 'ErrorReport'
     unless res
       addr, domain = HostUrl.outgoing_email_address.split(/@/)
-      res = "#{addr}+#{self.reply_to_secure_id}-#{self.id}@#{domain}"
+      res = "#{addr}+#{self.reply_to_secure_id}-#{self.global_id}@#{domain}"
     end
   end