DB2 client unreliable ("Needed to have 6 in buffer but only had 0")

[blafond]

There's an issue with the vert.x Db2 client that's causing the following exception when running the build:

 ERRORerrors [vert.x-eventloop-thread-0] HR000057: Failed to execute statement [select identifier0_.id as id1_0_, identifier0_.name as name2_0_ from IdentifierGenerationTypeTest$IntegerEntity identifier0_]: could not execute query
    java.util.concurrent.CompletionException: java.lang.IllegalStateException: Needed to have 6 in buffer but only had 0. In JDBC we would normally block here but need to find a non-blocking solution

We've created an issue on the Vert.x SQL client: #899

At the moment, we are making the build work by disabling the following tests for Db2:

• OrderedEmbeddableCollectionTest

• IdentifierGenerationTypeTest

Note that the error will only happen when running the full test suite. Running the single tests will work fine.

Some more tests are failing for the same error. See 25c0c18