Fix "ImproperlyConfigured" on master with TEST_NAME and TEST settings

The full error:

> ImproperlyConfigured: Connection 'default' has mismatched TEST and
TEST_* database settings.
Stab at fixing TestSqliteWithXdist: use conn.creation._get_test_db_name
Merge branch 'sqlite-filedb-support-in-tests' into integration

Conflicts:
	tests/test_db_setup.py
kwargs for create_test_db_with_reuse for Django 1.7/master