Clean up tables after each test.

Follow-Up to https://github.com/rails/rails/pull/14400

This ensures that all tables are removed after each test and thereby
allowing us to run the tests in a random order.
Adding active_model in Rails::Info
Merge pull request #14463 from ankit8898/add_info

Adding active_model in Rails::Info
Merge pull request #14440 from tgxworld/mysql_table_cleanup_after_each_test

Clean up tables after each test.
Remove sqlite3 lines from .gitignore if the application is not using sqlite3.
Merge pull request #14447 from Houdini/gitignore

Skip sqlite3 files in .gitignore if no sqlite3 in app
Check if any sqlite files are not included in the gitignore

If the sqlite file name change in future version we this regexp should
catch