scripted-diff: Rename sync_blocks to send_blocks to avoid name collisions and confusion

-BEGIN VERIFY SCRIPT-
FILE_LIST=$(git grep -l 'def sync_blocks' ./test/functional/*.py)
sed -i -e 's/def sync_blocks/def send_blocks/g'   $FILE_LIST
sed -i -e 's/self.sync_blocks/self.send_blocks/g' $FILE_LIST
-END VERIFY SCRIPT-

Author: MarcoFalke