With the test now ported to https://gitlab.apertis.org/tests/tumbler-thumbnailing


lets update the test template with new instructions to run the test

Signed-off-by: Andre Moreira Magalhaes (andrunko) <andre.magalhaes@collabora.co.uk>

- Update the README listing existing macros and how to
  use the renderer.
- Rename the main program to render-test-case
- Rename the tc directory to tests-cases

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>

- Add a new post-condition section.
- Add a new macro to install packages for automated tests.
- Slightly change the way the function to parse lists work. Now
  only the run.steps section will be treated different from
  other sections.
- Apply syntax changes to the already ported test cases.
- Add new ported test cases.
- Update the README explaining a rule for the formatter.

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>

This commit updates the remaining test cases with the supported
format.

It also adds a first macro to conveniently add common pre-conditions
for ostree test cases.

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>