Existing columns not found (at least in mysql)

Existing columns in the database were not found since dsn was being used instead of just the db name part of the dsn. 
Two examples where I ran into this
- Schema tool trying to create existing columns over and over again.
- Migrations not being able to set a primary key for columns created earlier.

Note that this fix is quite basic it might the case the conversion has to happen earlier on in the code for example by adding a 'getDatabaseName()' method to \Doctrine\DBAL\Connection or maybe just apply it in \Doctrine\DBAL\Platforms\MySqlPlatform::getListTableIndexesSQL()?

Please let me know