Sync to an RC2 build

[ChrisJollyAU]

EFCore RC2 introduces a significant change with the History Repository for the providers.

• Update to use the new way of locking the database for doing migrations
• NB: Override MigrationCommandExecutor with JetMigrationCommandExecutor
  • Base applies all migrations as part of a single transaction.
  • For some migrations (rename column/table) Jet doesn't have a SQL to do it so we have to step out and do it in ADOX/DAO
  • This requires the changes till then be committed.
  • Strategy is to ensure each group of migrations is committed before going to the next
  • Also for each group, make sure we split (if necessary) the commands so that those that need to be executed separately are in their own batch

Some other smaller fixes

• Some identity properties on a class mapped to json didn't get the correct ValueGenerated value
• Removed the handling of GO in the SQL of SqlOperation migrations. GO is a Sql Server specific command and is irrelevant to Jet