Set allow_mult=false on test bucket to prevent crash in test due to siblings 

Test was crashing because there was a sibling:

18:26:19.946 [warning] replication2 failed: {{badmatch,[{{dict,5,16,16,8,80,48,{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},{{[],[],[],[],[[cluster_of_record,65],[mutators_applied,riak_repl_reduced]],[],[],[],[],[],[[<<"X-Riak-VTag">>,49,56,48,120,83,112,53,109,69,74,74,48,81,108,99,103,112,115,82,74,86,70]],[[<<"index">>]],[],[[<<"X-Riak-Last-Modified">>|{1384,471557,44502}]],[],[]}}},<<0,0,3,132>>},{{dict,5,16,16,8,80,48,{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},{{[],[],[],[],[[cluster_of_record,65],[mutators_applied,riak_repl_reduced]],[],[],[],[],[],[[<<"X-Riak-VTag">>,49,77,106,107,69,52,66,83,102,73,83,80,116,87,68,57,104,82,75,69,74,57]],[[<<"index">>]],[],[[<<"X-Riak-Last-Modified">>|{1384,471562,248058}]],[],[]}}},<<0,0,3,132>>}]},[{riak_object,get_value,1,[{file,"src/riak_object.erl"},{line,355}]},{rt,'-systest_read/5-fun-0-',5,[{file,"src/rt.erl"},{line,942}]},{lists,foldl,3,[{file,"lists.erl"},{line,1197}]},{repl_util,'-wait_for_reads/5-fun-0-',6,[{file,"tests/repl_util.erl"},{line,142}]},{rt,wait_until,3,[{file,"src/rt.erl"},{line,511}]},{repl_util,wait_for_reads,5,[{file,"tests/repl_util.erl"},{line,140}]},{replication2,'-replication/3-fun-108-',3,[{file,"tests/replication2.erl"},{line,443}]},{replication2,replication,3,[{file,"tests/replication2.erl"},{line,443}]}]}
18:26:19.947 [error]