*: show create table output utf8_bin collate.
We only support case sensitive utf8_bin collation right now, but show create table ignored the collation.
So the dumped DDL statement doesn't contains collation option.
When the DDL statement is executed on MySQL, the collation will be changed to utf8_general_ci.
If the string column is defined as unique key, there would be duplicated key error.
This PR enforce utf8 charset and utf8_bin collation when parse a column definition, and enfore table option
`DEFAULT CHARSET=utf8 COLLATE=utf8_bin` in SHOW CREATE TABLE statement.