DB driver specific options are missed in help output

[Alexey Stroganov]

Help section of sysbench-0.5 doesn't contain information about driver specific options.

In sysbench-0.4 we have:

./sysbench-0.4.13 --test=oltp help
...

mysql options:
  --mysql-host=[LIST,...] MySQL server host [localhost]
  --mysql-port=N MySQL server port [3306]
  --mysql-socket=STRING MySQL socket
  --mysql-user=STRING MySQL user [sbtest]
  --mysql-password=STRING MySQL password []
  --mysql-db=STRING MySQL database name [sbtest]
  --mysql-table-engine=STRING storage engine to use for the test table {myisam,innodb,bdb,heap,ndbcluster,federated} [innodb]
  --mysql-engine-trx=STRING whether storage engine used is transactional or not {yes,no,auto} [auto]
  --mysql-ssl=[on|off] use SSL connections, if available in the client library [off]
  --myisam-max-rows=N max-rows parameter for MyISAM tables [1000000]
  --mysql-create-options=STRING additional options passed to CREATE TABLE []
...

Info about above options are missed in sysbench 0.5