ISIS-2158: smoketests to have their individual in-mem connections
- adds new 'IsisPresets.H2InMemory_withUniqueSchema'
- also converts DN plugin to use new config bean 'DataNucleusSettings'
However, there might be a random number collision when generating unique
schema names, though highly unlikely. Unfortunately using a UUID as
schema name does not seem to work, its too long (has too many
characters).