fixed bug, when we change group_name select element, the optgroup of optgroup-oracle on instance_name select element never been set to empty.
if (data.status === 0) {
var result = data['data'];
$("#optgroup-mysql").empty();
+ $("#optgroup-oracle").empty();
$("#optgroup-mssql").empty();
$("#optgroup-redis").empty();
$("#optgroup-pgsql").empty();
