Fixed #27436 -- Fixed makemigrations crash when creating migrations on a separate drive than where Django is installed.

If the test user creation fails here, _create_test_db() would return without
switching to the test user which caused the tests to run using the main
connection instead of the test user.

Reverted test changes in a7a7ecd2 and
e43ea36b (refs #27025).

Thanks Yuriy Korobko for the initial patch and Tobias McNulty for review.

(Fixed #23604 in 2014 and was not added before.)

Thanks samuller for the report and initial patch.

'CASCADE' is an undocumented no-op in MySQL, so to avoid confusion Django no longer outputs it.

This is a security fix.

This is a security fix.