Unit Tests: one $factory to rule them all, and it shall be static.

Using more than one instance of `WP_UnitTest_Factory` causes all kinds of craziness, due to out-of-sync internal generator sequences. Since we want to use `setUpBeforeClass`, we were creating ad hoc instances. To avoid that, we were injecting one `static` instance via Dependency Injection in `wpSetUpBeforeClass`. All tests should really use the `static` instance, so we will remove the instance prop `$factory`.

Replace `$this->factory` with `self::$factory` over 2000 times.
Rewrite all of the tests that were hard-coding dynamic values. 

#YOLOFriday



git-svn-id: https://develop.svn.wordpress.org/trunk@35225 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/testcase-xmlrpc.php

@@ -22,7 +22,7 @@ class WP_XMLRPC_UnitTestCase extends WP_UnitTestCase {
 	}
 
 	protected function make_user_by_role( $role ) {
-		return $this->factory->user->create( array(
+		return self::$factory->user->create( array(
 			'user_login' => $role,
 			'user_pass'  => $role,
 			'role'       => $role