global: iter_suites overlay usage

• Allow iter_suites to be more easily used from overlays.

• NOTE Adds deprecation warning to import_module_from_packages and import_submodules_from_packages.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>