tests: functional: Wait for installation to complete fully

- There is a special page which is served when race condition occurs between the
setup middleware and setup view soon after an installation. In this case, a
special page is shown with 'App installed' as message but this is still the
setup view. Detect this case and wait for page to refresh.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/templates/setup.html

@@ -15,7 +15,9 @@
 
   {% if setup_state.value == 'up-to-date' %}
 
-     {% trans "Application installed." %}
+     <div class="app-just-installed">
+       {% trans "Application installed." %}
+     </div>
 
   {% elif not operations %}
 

plinth/tests/functional/__init__.py

@@ -342,7 +342,8 @@ def install(browser, app_name):
     install_button_css = '.form-install input[type=submit]'
     while True:
         script = 'return (document.readyState == "complete") && ' \
-            '(!Boolean(document.querySelector(".app-operation")));'
+            '(!Boolean(document.querySelector(".app-operation"))) &&' \
+            '(!Boolean(document.querySelector(".app-just-installed")));'
         if not browser.execute_script(script):
             time.sleep(0.1)
         elif browser.is_element_present_by_css('.neterror'):