add Identity() for remaining examples

add Identity() for remaining examples

Fixed the performance example scripts in examples/performance to mostly
work with the Oracle database, by adding the :class:`.Identity` construct
to all the tables and allowing primary generation to occur on this backend.
A few of the "raw DBAPI" cases still are not compatible with Oracle.

Change-Id: I7ce19645ea78736dddfda6f33b9356ad75dee68f
(cherry picked from commit 6e0a35dfd8bbd12c999abcae3309fe22e83b0444)