Fix for update stream test.

@sougou, @alainjobart, @ryszard 

This includes
  * fix for mysql.patch to fix the vt_mysqlbinlog binary. Needs bootstrap to be run again.
  * Fixes the bson encoding for update stream by using named variables rather than embedded variables.
  * Corresponding change in py/vtdb/update_stream_service.py and rowcache_invalidator.go