feature: Unit test to validate the db schema (#6367)

* Unit test to validate the db schema
Changes build-schema.php to just write misc/db_schema.yaml

* Only build base if needed
Fix 178.sql

* Database is always created by init.php
add dbSchema test too, should guard against testing against an empty database

* feature: support non-standard unix socket (#5724)

* Add support for custom MySQL unix-socket

* NULL must be lowercase!

* Naive edit of html/install.php

* fixup

* Refactor dbConnect
Use it everywhere

* $config needs to be global
Don't need to set $database_link

* small cleanups

* Connect to the database for every test.

* travis fix for blank line

sql-schema/178.sql

@@ -1 +1 @@
-ALTER TABLE `users` MODIFY `updated_at` TIMESTAMP;
+ALTER TABLE `users` MODIFY `updated_at` TIMESTAMP DEFAULT CURRENT_TIMESTAMP;