core: Replace log4j with slf4j in restapi

Replaces log4j with slf4j in restapi module.

Change-Id: I8109622c54eb2093753ab0c087d0d73d177aaa5a
Bug-Url: https://bugzilla.redhat.com/1109871
Signed-off-by: Martin Perina <mperina@redhat.com>