The kitchen-salt provisionner have the `pillars_from_directories`
option to recusively copy directories under target pillar root.
This has 3 advantages:
- simplify `kitchen.yml`
- manage pillar assignment with standard salt targetting mechanism,
this avoid the dedicated `gentoo` suite (it could have been done
from `kitchen.yml` itself by the way)
- ease the test outside kitchen by running `salt-call` directly with
`--pillar-root` like:
```
salt-call --local --id test-minion.example.net \
--file-root=template-formula/ \
--pillar-root=template-formula/test/salt/pillar/ \
state.show_sls TEMPLATE
```
* pillar.example: remove settings for testing purpose.
* test/salt/pillar/top.sls: limit `gentoo` pillars based on `os_family`
grain.
* test/salt/pillar/defaults.sls: base pillar dedicated to tests.
* kitchen.yml (suites): remove the now useless `gentoo` suite.
Define `pillars_from_directories` to copy them under `pillar_root`.
Remove useless `pillars_from_files`.
* .gitlab-ci.yml: fix gentoo suite name
* .gitignore: do not ignore test pillar `top.sls`
