Port Cheetah templates to Jinja2

Cheetah is unmaintained since 2010 and it's unlikely to get Python3
support soon. Also, the rest of OpenStack (mostly) standardized on
Jinja2.

Implements: blueprint jinja-templating-conversion
Change-Id: Ia15f00ee96d3c1d55d7c290f20ccc988e4c52e1a
Merge "Port Cheetah templates to Jinja2"