core : [AAA] NPE is raised when searching user in domain by lastname

NPE when searching for user by lastname. SearchQuery
passes $SN for lastname as key but the map in
SearchQueryParsingUtils is missing $SN as key
for the attributes map

Change-Id: I294d415201f155d263d588b5a21f803c0870cb95
Bug-Url: https://bugzilla.redhat.com/1117240
Signed-off-by: Ravi Nori <rnori@redhat.com>