Covers issues with CID: 34674, 41851, 69795, 71862, 71881, 71882

A new defect has been detected and assigned to renctan in Coverity Connect.
http://coverity.mongodb.com//sourcebrowser.htm?projectId=10001#mergedDefectId=71882
The defect was flagged by checker CHECKED_RETURN in
file /src/mongo/s/commands/cluster_write_cmd.cpp
function mongo::<unnamed>::ClusterWriteCmd::run(mongo::OperationContext *, const std::basic_string<char, std::char_traits<char>, std::allocator<char>>&, mongo::BSONObj &, int, std::basic_string<char, std::char_traits<char>, std::allocator<char>>&, mongo::BSONObjBuilder &, bool)
and this ticket was created by renctan