diagnostics: Implement diagnostics for Plinth

- Note that while Plinth is running or not running, diagnostics can be
  run on the command line with --diagnose option to Plinth binary.  That
  makes these tests just as useful as freedombox-setup testsuite.

plinth/modules/diagnostics/__init__.py

@@ -21,7 +21,19 @@ Plinth module for system diagnostics
 
 from . import diagnostics
 from .diagnostics import init
+from plinth import action_utils
 
 __all__ = ['diagnostics', 'init']
 
 depends = ['plinth.modules.system']
+
+
+def diagnose():
+    """Run diagnostics and return the results."""
+    results = []
+    results.append(action_utils.diagnose_port_listening(8000, 'tcp4'))
+    results.append(action_utils.diagnose_port_listening(8000, 'tcp6'))
+    results.extend(action_utils.diagnose_url_on_all(
+        'http://{host}/plinth/', extra_options=['--no-check-certificate']))
+
+    return results

plinth/modules/diagnostics/urls.py

@@ -25,7 +25,6 @@ from django.conf.urls import patterns, url
 urlpatterns = patterns(  # pylint: disable-msg=C0103
     'plinth.modules.diagnostics.diagnostics',
     url(r'^sys/diagnostics/$', 'index', name='index'),
-    url(r'^sys/diagnostics/test/$', 'test', name='test'),
-    url(r'^sys/diagnostics/module/(?P<module_name>[a-z\-]+)/$', 'module',
+    url(r'^sys/diagnostics/(?P<module_name>[a-z\-]+)/$', 'module',
         name='module'),
     )