extapi: provide configuration file name

this will enable extension to use relative file names.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1158775
Change-Id: Ie380f38f1ef6a68bdfa58c3b17ab26ed0fbb37b3
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>