flatpak: add tests in CI, add no_dependencies parameter (#2751)

* Similar version restrictions than flatpak_remote tests.

* ...

* Try to work around missing dependencies.

* Revert "Try to work around missing dependencies."

This reverts commit 66a4e38566.

* Add changelog.

* App8 -> App2; make sure that there are two apps App1 and App2.

* Fix forgotten variabe.

* Remove test notices.

* Seems like flatpak no longer supports file:// URLs.

The tests would need to be rewritten to offer the URL via http:// instead.

* Try local HTTP server for URL tests.

* ...

* Lint, add status check.

* Add boilerplate.

* Add 'ps aux'.

* Surrender to -f.

* Work around apparent flatpak bug.

* Fix YAML.

* Improve condition.

* Make sure test reruns behave better.

tests/integration/targets/flatpak/aliases

@@ -1,4 +1,4 @@
-unsupported
+shippable/posix/group3
 destructive
 skip/aix
 skip/freebsd
@@ -6,4 +6,3 @@ skip/osx
 skip/macos
 skip/rhel
 needs/root
-needs/privileged