Convert user_cancel_method variable to CMI system

This patch looks basically fine, just a few whitespace issues:

+++ b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsAdminTest.phpundefined
@@ -137,8 +137,8 @@ class StatisticsAdminTest extends WebTestBase {
-    variable_set('user_cancel_method', 'user_cancel_delete');
+    ¶

There's a few leading whitespace issues like this.

+++ b/core/modules/user/user.admin.incundefined
@@ -654,6 +655,7 @@ function user_admin_settings_submit($form, &$form_state) {
     ->set('signatures', $form_state['values']['user_signatures'])
+    ->set('cancel_method', $form_state['values']['user_cancel_method'])      ¶

Trailing whitespace here.

I will post a patch shortly...

Cleaned up the whitespace stuff.

It probably wouldn't hurt to add some basic test coverage for this, see SystemUpgradePathTest.php (we should rename that to ConfigUpgradePathTest in another issue). Then we don't have to test it manually to RTBC this.

Ok so I have added an upgrade path, and set the default for the value in user.settings.yml instead of using a ternary.

There's an unused variable, $default_method, in user_cancel_confirm_form(), which is in D7 as well, so I wil create an issue for that once this gets committed.

Issue created to rename the test class: #1825648: Rename SystemUpgradePathTest to ConfigUpgradePathTest, so we can have tests for the CMI upgrade path

Not sure if we need a separate test method for this, because it's the same database dump anyway. Other than that, this looks good to me.

Moved tests into same method, renamed, and updated comment.

Yes, I think this is fine like this.

Looks good. Committed/pushed to 8.x.

Great stuff. I have posted a patch over in #1825648: Rename SystemUpgradePathTest to ConfigUpgradePathTest, so we can have tests for the CMI upgrade path, if we can get that or something similar in it will be a good conduit to increasing test coverage of the conversion effort.