The new master branch should point now to rocky.
So, HOT templates should specify that they might contain features
for rocky release [1]
Also, this submission updates the yaml validation to use only latest
heat_version alias. There are cases in which we will need to set
the version for specific templates i.e. mixed versions, so there
is added a variable to assign specific templates to specific heat_version
aliases, avoiding the introductions of error by bulk replacing the
the old version in new releases.
[1]: https://docs.openstack.org/heat/latest/template_guide/hot_spec.html#rocky
Change-Id: Ib17526d9cc453516d99d4659ee5fa51a5aa7fb4b
44ef2a3ec1