Use capitalized prefix for status variable

Because MariaDB 10.0.2 starts to auto capitalize the first chracter in
"SHOW STATUS". We don't want to maintain two expected test
results (for MySQL and MariaDB < 10.0.2 and for MariaDB >= 10.0.2). So
we use capitalized status variable name by default.

It will not be any negative effect for query because "SHOW STATUS
LIKE" is case insensitive. It may have negative effect for getting
variable if a MySQL client compares case sensistive.

Capitalized status variable name is MySQL way naming rule. See other
status variable such as Uptime.