Feature Request: Add support for YAML test input file and Jinja2 scheduler job templates

[hagertnl]

It would be really useful to add YAML file format for the test input file (rgt_test_input.yaml), and at the same time enable Jinja2 templates for the scheduler job template. This would enable several really useful possibilities:

1. Instead of a single string, the build_cmd and check_cmd could possibly actually be a list of commands to run
2. More powerful templating format in the job script (the __ notation is a bit clunky sometimes). Jinja allows things like iterating over a list
3. .yaml is more widely used than .ini in most tools today