The following tests added:
- depmod_search_order_external_first -- checks if external module
is taken in use when it has higher priority;
- depmod_search_order_external_last -- checks if external module
is skipped when it has lower priority;
- test_modinfo_external -- checks if modinfo is able to look up
correct external module;
- modprobe_external -- checks if modprobe is able to look up
correct external module and loads it.
Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>