extapi: use collection instead of list

primitive types are better, no real reason to use list in these.

Topic: AAA
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1120720
Change-Id: I0555f7f10bae370c3605b5253cab09620ff770bb
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>