Describe the current, buggy behavior

Several wp db * commands don't work with sqlite.

SQLite is in testing fase

Describe how other contributors can replicate this bug

• Install a new WP,
• wp plugin install performance-lab --activate
• In the performance-lab plugin settings activate the sqlite setting.
• wp-content/databases/.ht.sqlite should exist.
• wp db drop --yes the mysql gets dropped,
  This is fine for this test to make sure you don't read the mysql.
  But shouldn't it drop the sqlite file?
• Click around in the admin/frontend. The website WordPress still works.
• wp post list
  Shows the hello world
• wp db query "SELECT * FROM wp_posts;"
  Gives an error.
• wp db search 'hello'
  Does work, with a warning.

It appears wp-content/db.php doesn't get loaded.
I don't know when/where it should be included. And if it even would help.

Keep in mind, FQDBDIR and FQDB constants can be set to change the location & filename of the sqlite file.