Improve database messages in persistence setup command

Currently, if a users chooses a database other than hsqldb or H2, a message appears directing the user to enter their database details in either the database.properties or persistence.xml (when DataNucleus is selected). However this message is displayed before the persistence setup command is fully executed and other Roo update messages can follow which looks strange as well being confusing. This change will move the messages from the JpaOperationsImpl class to the JpaCommands class and only appear after the call to JpaOperations.configureJpa() is completed. Also, it will decrease clutter in the JpaOperationsImpl class and centralise the logic in one spot.