SqlServerOptimisticConcurrencyTests fail if run without an existing data...

...base, being unable to insert values in the Id columns, when seeding the database, because they are marked with IDENTITY. The fix replicates logic from SqlServerValueGeneratorSelector to determine whether the column corresponding to a property needs to be marked with IDENTITY or not.

Replicated logic from SqlServerValueGeneratorSelector in SqlServerMigrationOperationFactory.Column(IProperty property) and removed IPropertyExtensions.IsIdentity