Fix "common" user creation on Oracle 12c+.

[Moritz Schaffenroth]

Hi,

when running the tests on django 3.0 against a Oracle 12c database i get the following errors:

python manage.py test
Creating test database for alias 'default'...
Failed (ORA-01543: tablespace 'TEST_A_GUI' already exists)
It appears the test database, test_A_GUI, already exists. Type 'yes' to delete it, or 'no' to cancel: yes
Destroying old test database for alias 'default'...
Creating test user...
Failed (ORA-65096: invalid common user or role name)
Got an error creating the test user: ORA-65096: invalid common user or role name

This seems to be the following problem:
​https://stackoverflow.com/questions/57952435/django-tutorial-testcase-failed-to-create-testuser-on-oracle-express-database
The solution can be found here: ​https://stackoverflow.com/questions/33330968/error-ora-65096-invalid-common-user-or-role-name-in-oracle
It is to execute the following sql before creating the user:
alter session set "_ORACLE_SCRIPT"=true;
I created a pull request for this issue:
​https://github.com/django/django/pull/12301

BR,
Moritz

[Mariusz Felisiak]

You don't need to use this undocumented parameter when you create a local users at the PDB level, what you should do. IMO we shouldn't support creating test "common" users, see ​article for details.