Add DB2 10.5 Support

This patch adds the initial support for DB2 10.5 to migrate. It
includes:

1. The dialect implementation for DB2.
2. The dialect registration with the visitor.
3. Code to parse the engine name in version.py.
4. A new dependency on ibm_db_sa in test-requirements.txt.
5. A connection string in test_db.cfg for ibm_db_sa.

Part of blueprint add-db2-support

Co-authored-by: Sheng Bo Hou <sbhou@cn.ibm.com>
Co-authored-by: Thuy Christenson <thuy@us.ibm.com>
Co-authored-by: Rahul Priyadarshi <rahul.priyadarshi@in.ibm.com>
Change-Id: I745ec615487b1b06c5d1a09ea316f376d66ee4c0
Merge "Add DB2 10.5 Support"