Skip test if the MySQL driver is not available.

  $ if [ -z "$SBTEST_HAS_MYSQL" ]
  > then
  >   exit 80
  > fi

  $ sysbench --help | grep -- '--db-driver'
    --db-driver=STRING  specifies database driver to use ('help' to get list of available drivers) [mysql]

  $ sysbench --help | sed -n '/mysql options:/,/^$/p' | grep -v 'mysql-ssl[=\[]'
  mysql options:
    --mysql-host=[LIST,...]               MySQL server host [localhost]
    --mysql-port=[LIST,...]               MySQL server port [3306]
    --mysql-socket=[LIST,...]             MySQL socket
    --mysql-user=STRING                   MySQL user [sbtest]
    --mysql-password=STRING               MySQL password []
    --mysql-db=STRING                     MySQL database name [sbtest]
    --mysql-ssl-key=STRING                path name of the client private key file
    --mysql-ssl-ca=STRING                 path name of the CA file
    --mysql-ssl-cert=STRING               path name of the client public key certificate file
    --mysql-ssl-cipher=STRING             use specific cipher for SSL connections []
    --mysql-compression[=on|off]          use compression, if available in the client library [off]
    --mysql-compression-algorithms=STRING compression algorithms to use [zlib]
    --mysql-debug[=on|off]                trace all client library calls [off]
    --mysql-ignore-errors=[LIST,...]      list of errors to ignore, or "all" [1213,1020,1205]
    --mysql-dry-run[=on|off]              Dry run, pretend that all MySQL client API calls are successful without executing them [off]