tests: move enter_keys_in_window to base SystemTestsMixin class

This ways it will be available also in DispVM tests (already referenced
there), and others.

tests/__init__.py

@@ -361,6 +361,24 @@ class SystemTestsMixin(object):
                 )
             time.sleep(0.1)
 
+    def enter_keys_in_window(self, title, keys):
+        """
+        Search for window with given title, then enter listed keys there.
+        The function will wait for said window to appear.
+
+        :param title: title of window
+        :param keys: list of keys to enter, as for `xdotool key`
+        :return: None
+        """
+
+        # 'xdotool search --sync' sometimes crashes on some race when
+        # accessing window properties
+        self.wait_for_window(title)
+        command = ['xdotool', 'search', '--name', title,
+                   'windowactivate',
+                   'key'] + keys
+        subprocess.check_call(command)
+
     def shutdown_and_wait(self, vm, timeout=60):
         vm.shutdown()
         while timeout > 0:

tests/vm_qrexec_gui.py

@@ -54,24 +54,6 @@ class TC_00_AppVMMixin(qubes.tests.SystemTestsMixin):
         self.testvm1 = self.qc[self.testvm1.qid]
         self.testvm2 = self.qc[self.testvm2.qid]
 
-    def enter_keys_in_window(self, title, keys):
-        """
-        Search for window with given title, then enter listed keys there.
-        The function will wait for said window to appear.
-
-        :param title: title of window
-        :param keys: list of keys to enter, as for `xdotool key`
-        :return: None
-        """
-
-        # 'xdotool search --sync' sometimes crashes on some race when
-        # accessing window properties
-        self.wait_for_window(title)
-        command = ['xdotool', 'search', '--name', title,
-                   'windowactivate',
-                   'key'] + keys
-        subprocess.check_call(command)
-
     def test_000_start_shutdown(self):
         self.testvm1.start()
         self.assertEquals(self.testvm1.get_power_state(), "Running")