This was found via MDL-67886

There are small edge cases where certain plugins need to have different schemas depending on which db they are using. This will cause the schema check to fail on the other db's.

The root cause here is that we have no way of declaring in the xml file that a chunk only applies for a certain db driver. The environment.xml format does have this expressive power so in we could extend xmldb to do something similar such as:

<INDEXES>

    <VENDOR name="postgres">

        <INDEX NAME="name" UNIQUE="false" FIELDS="fiedl1,field2" COMMENT="Some index"/>

     <VENDOR>

</INDEXES>