select_statement: return exceptions as errors in execute_without_checking_exception_message
select_statement: return exceptions as errors in execute_without_checking_exception_message

Modifies the remaining logic of execute_without... (apart from the
do_execute call) so that the result-aware versions of storage_proxy's
methods are called and failed results are converted to
result_message::exception.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla