refs #54: add tests for TIMESTAMP WITH TIME ZONE

[KengoTODA]

To ensure that we can use getInstant(int) if we use TIMESTAMP WITH TIME ZONE.

[Narigo]

Hi @KengoTODA - sorry for the late response in the bug report. Can you rebase the test against the latest master (incorporating the fix by @pmlopes)? I'd be happy to merge this test. If you want to make it even better, try to move it into SQLTestBase so both PostgreSQL and MySQL check this property. But I can do that afterwards, if you want :)
Thanks!

[KengoTODA]

@Narigo Thanks for your comment! I tried but I found that WITH TIME ZONE is invalid for MySQL.
Can I keep this test in PostgreSQLTest? Then I'll solve conflict later.

testInstantWithTimeZone(io.vertx.ext.asyncsql.MySQLClientTest)  Time elapsed: 0.017 sec  <<< ERROR!
com.github.mauricio.async.db.mysql.exceptions.MySQLException: Error 1064 - #42000 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'TIME ZONE)' at line 1
    at com.github.mauricio.async.db.mysql.MySQLConnection.onError(MySQLConnection.scala:126)