Fixed TransactionalTests.test_password_with_at_sign() isolation on Oracle.

[felixxm]

Without this patch:

python runtests.py backends.oracle.tests.TransactionalTests.test_password_with_at_sign
Testing against Django installed in '/django/django' with up to 8 processes
Found 1 test(s).
Creating test database for alias 'default'...
Creating test user...
System check identified no issues (0 silenced).
F
======================================================================
FAIL: test_password_with_at_sign (backends.oracle.tests.TransactionalTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/django/tests/backends/oracle/tests.py", line 113, in test_password_with_at_sign
    with self.assertRaises(DatabaseError) as context:
AssertionError: DatabaseError not raised

----------------------------------------------------------------------

----------------------------------------------------------------------
Ran 1 test in 0.544s

FAILED (failures=1)
Destroying test database for alias 'default'...
Destroying test user...
Destroying test database tables...

With the patch:

python runtests.py backends.oracle.tests.TransactionalTests.test_password_with_at_sign
Testing against Django installed in '/django/django' with up to 8 processes
Found 1 test(s).
Creating test database for alias 'default'...
Creating test user...
System check identified no issues (0 silenced).
.
----------------------------------------------------------------------
Ran 1 test in 2.132s

OK
Destroying test database for alias 'default'...
Destroying test user...
Destroying test database tables...

[felixxm]

buildbot, test on oracle.

[nessita]

Question, is this new local import part of the solution? From the code it looks like oracle's DatabaseError is not an child of Django's DatabaseError?

[nessita]

Other than my question (to better understand the fix), LGTM 👍

[felixxm]

We need to catch a different error, because we're calling a different method that doesn't wrap database-specific errors with Django's DatabaseError.

[felixxm]

buildbot, test on oracle.

[felixxm]

Thanks both for checking 👍