title: H2 in Oracle compatibility mode is validated as H2, not oracle
body: <p>In production I'm using Oracle and all my changelogs have been written with Oracle in mind.
  In my development environment I'm trying to generate the changelogs on an H2 instance in Oracle compatibility mode. 
  This is to improve integration test speed.</p>
  
  <p>My problem is that Liquibase is validating my changelogs against H2, not Oracle.
  Is there a way of forcing Liquibase to validate against Oracle even though my db url looks like an H2 one?</p>
  
  <p>My biggest headaches are regarding sequences and dropNotNullConstraint validations.</p>
  
  <p><strong>Liquibase version:</strong> 2.0.5 (I also tried with 3.1.1, same issue)</p>
  
  <p><strong>H2 connection url:</strong> jdbc:h2:tcp://localhost:9092/test;MODE=Oracle;AUTO_SERVER=TRUE;DB_CLOSE_DELAY=-1</p>
  
  <p>I'm pretty sure this is a common scenario so I guess I'm probably doing something wrong?</p>
  
  <p>any help would be greatly appreciated</p>