Create a model hook around the lockable warden hook to reset attempts

Resetting failed attempts after sign in happened inside a warden hook
specific for the lockable module, but that was hidden inside the hook
implementation and didn't allow any user customization.

One such customization needed for example is to direct these updates to
a write DB when using a multi-DB setup. With the logic hidden in the
warden hook this wasn't possible, now that it's exposed in a model
method much like trackable, we can override the model method to wrap it
in a connection switch block for example, point to a write DB, and
simply call `super`.

Closes #5310
Related to #5264 and #5133

test/models/lockable_test.rb

@@ -50,6 +50,32 @@ class LockableTest < ActiveSupport::TestCase
     assert_equal initial_failed_attempts + 2, user.reload.failed_attempts
   end
 
+  test "reset_failed_attempts! updates the failed attempts counter back to 0" do
+    user = create_user(failed_attempts: 3)
+    assert_equal 3, user.failed_attempts
+
+    user.reset_failed_attempts!
+    assert_equal 0, user.failed_attempts
+
+    user.reset_failed_attempts!
+    assert_equal 0, user.failed_attempts
+  end
+
+  test "reset_failed_attempts! does not run model validations" do
+    user = create_user(failed_attempts: 1)
+    user.expects(:after_validation_callback).never
+
+    assert user.reset_failed_attempts!
+    assert_equal 0, user.failed_attempts
+  end
+
+  test "reset_failed_attempts! does not try to reset if not using failed attempts strategy" do
+    admin = create_admin
+
+    refute_respond_to admin, :failed_attempts
+    refute admin.reset_failed_attempts!
+  end
+
   test 'should be valid for authentication with a unlocked user' do
     user = create_user
     user.lock_access!