Multiple instances of Flyway, DB2 z/OS

Hello,

I tried your approach, (substr(5) + counter starting at 000) and I tried to keep the change in createMetaDataTable.sql for db2zos. But it is not possible to use functions or operations in the name-part of a DDL. So I had to look for another solution. 

The pull request contains a solution using placeholders from Java. The drawback with this is that I use db2zos-spesific code in MetaDataTableImpl.java. I SHA the tablename instead of using a counter. Then I can  bypass a database query to check if a metadata-table already exists. 

It would be nice if you can look at it and give some feedback

kind regards
Christine