Introduce env variable KWIN_XKB_DEFAULT_KEYMAP to force default layout creation

Summary:
The Xkb class loads keyboard layouts from the users configuration. This
makes tests fail locally if the user has a layout which behaves
differently to the one the test expects. E.g. on a German layout the
right alt key is different to the one of US layout.

In order to have a more stable test base the env variable
KWIN_XKB_DEFAULT_KEYMAP forces the loading of the default keymap, thus
tests have a common layout set.

Reviewers: #kwin, #plasma_on_wayland

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D2466

autotests/integration/modifier_only_shortcut_test.cpp

@@ -92,6 +92,7 @@ void ModifierOnlyShortcutTest::initTestCase()
     QVERIFY(waylandServer()->init(s_socketName.toLocal8Bit()));
 
     kwinApp()->setConfig(KSharedConfig::openConfig(QString(), KConfig::SimpleConfig));
+    qputenv("KWIN_XKB_DEFAULT_KEYMAP", "1");
 
     kwinApp()->start();
     QVERIFY(workspaceCreatedSpy.wait());

keyboard_input.cpp

@@ -118,7 +118,10 @@ void Xkb::reconfigure()
         return;
     }
 
-    xkb_keymap *keymap = loadKeymapFromConfig();
+    xkb_keymap *keymap = nullptr;
+    if (!qEnvironmentVariableIsSet("KWIN_XKB_DEFAULT_KEYMAP")) {
+        keymap = loadKeymapFromConfig();
+    }
     if (!keymap) {
         qCDebug(KWIN_XKB) << "Could not create xkb keymap from configuration";
         keymap = loadDefaultKeymap();