Remove test file and create a format directory

- Remove the install-tests-cases.yaml test definition. This was
  only used for testing how to install test cases in lava.
- Move the format definition and template to the format/ dir.

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

install-tests-cases.yaml

-metadata:
-  name: install-tests-cases
-  format: "Lava Test Definition 1.0"
-  description: "Install test cases"
-
-run:
-  steps:
-    - lava-test-case create-tests-cases-dir --shell mkdir -R /var/lib/tests_cases/
-    - lava-test-case install-tests-cases --shell cp tc/* /var/lib/tests_cases/