merge.py use a class to represent template syntax

Defining cfn template syntax as class attributes will make it easier
to port merge.py to HOT just by setting lang to a different class.

Change-Id: I2547333d727bf91cd3159790f0f20f4d10195a9c
Partial-Blueprint: tripleo-juno-remove-mergepy
Merge "merge.py use a class to represent template syntax"