Assign OS390Reflector for Db2 for z/OS (#147)

When connecting to a DBMS starting with "DSN" (Db2 for z/OS), assign the OS390Reflector.

Signed-off-by: R_H <118392077+rhgit01@users.noreply.github.com>

Author: rhgit01

ibm_db_sa/base.py

@@ -733,6 +733,8 @@ def initialize(self, connection):
             _reflector_cls = ibm_reflection.DB2Reflector
         elif "IDS/" in self.dbms_name:
             _reflector_cls = ibm_reflection.DB2Reflector
+        elif self.dbms_name.startswith("DSN"):
+            _reflector_cls = ibm_reflection.OS390Reflector            
         self._reflector = _reflector_cls(self)
 
     def get_columns(self, connection, table_name, schema=None, **kw):