Look at using p2cli in grafana

[timothyb89]

We recently started including Python in our grafana images to process templates with jinja2. This caused a ~50% increase in the size of the image.

p2cli potentially provides the same functionality at 1/4th the size, so we should look at using it instead. We already use this utility in the log agent: https://github.com/monasca/monasca-docker/blob/master/monasca-log-agent/Dockerfile#L36

[matrixik]

When looking into #328 I found that p2cli is not simple replacement for Jinja2. It's implementing Django templates and there are some differences but I still think that this is still better than including whole Python with Jinja2.