restapi: aaa: fix coverity issue, default encoding

Topic: AAA
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1120720
Change-Id: I5de36d41c23d548fb4a6d91902cbd00f358e09c5
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>