oslo.db doesn't handle sqlite dupe key error correctly

[Oleksii Chuprykov]

Steps to reproduce:
target platform: cent os 6.5

>>> from oslo.db.sqlalchemy import session
>>> eng = session.create_engine('sqlite://')
>>> eng.execute('create table t(a integer primary key)')
<sqlalchemy.engine.result.ResultProxy object at 0x1dbe1d0>
>>> eng.execute('insert into t values(10)')
<sqlalchemy.engine.result.ResultProxy object at 0x1dbe850>
>>> eng.execute('insert into t values(10)')
No handlers could be found for logger "oslo.db.sqlalchemy.exc_filters"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1751, in execute
    return connection.execute(statement, *multiparams, **params)
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 721, in execute
    return self._execute_text(object, multiparams, params)
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 870, in _execute_text
    statement, parameters
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 958, in _execute_context
    context)
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1155, in _handle_dbapi_exception
    util.raise_from_cause(newraise, exc_info)
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/util/compat.py", line 199, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 951, in _execute_context
    context)
  File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/default.py", line 436, in do_execute
    cursor.execute(statement, parameters)
oslo.db.exception.DBError: (IntegrityError) PRIMARY KEY must be unique 'insert into t values(10)' ()

We get exception.DBError instead of exception.DBDuplicateEntry
http://logs.openstack.org/69/128669/1/check/gate-cinder-python26/0180d83/testr_results.html.gz

[Roman Podoliaka (rpodolyaka)]

Fixed by https://review.openstack.org/#/c/131095/