Issue #2249723 by andrei.dincu: Update all tests and get object services as variables instead of calling \Drupal::* every time

Issue #2249723 by andrei.dincu: Set state() variables in hook_install() makes XmlSitemapNodeFunctionalTest passes all tests

Issue #2249723 by andrei.dincu: Move XmlSitemapI18nNodeTest to XmlSitemapMultilingualNodeTest, XmlSitemapI18nTest to XmlSitemapMultilingualTest and XmlSitemapI18nWebTestCase to XmlSitemapMultilingualTestBase

Issue #2249723 by andrei.dincu: Move XmlSitemapTestHelper to XmlSitemapTestBase, add phpdoc for some test classes and make helper test classes abstract

Issue #2249723 by andrei.dincu: Save config() variables when they are changed in XmlSitemapTestHelper

Issue #2249723 by andrei.dincu: Replace XML with Xml in class name for XmlSitemapI18nNodeTest and XmlSitemapI18nTest

Issue #2249723 by andrei.dincu: Do not store sitemap entities values in state(), store them in config()

Issue #2249723 by andrei.dincu: XmlSitemapTestHelper get sitemap uri with xmlsitemap_sitemap_uri() function

Issue #2249723 by andrei.dincu: D8 code updates in XmlSitemapUserFunctionalTest, XmlSitemapNodeFunctionalTest and XmlSitemapRobotsTxtIntegrationTest

Issue #2249723 by andrei.dincu: Create XmlSitemapUserFunctionalTest class to test xmlsitemap_user feature

Issue #2249723 by andrei.dincu: Replace variable_set() with D8 code in XmlSitemapUnitTest and XmlSitemapTestHelper