base-manager: allow forcing the testing without udev

Even if udev support is really built and available.

This is extremely useful to test the udev-less setup without fully
recompiling the whole daemon.

  E.g.: the daemon can be run like this:
    $ sudo /usr/sbin/ModemManager --debug --test-no-udev

  And then, the kernel events may be reported using mmcli like this:
    $ sudo mmcli --report-kernel-event-auto-scan

src/mm-context.c

@@ -222,6 +222,9 @@ mm_context_get_log_relative_timestamps (void)
 static gboolean  test_session;
 static gboolean  test_enable;
 static gchar    *test_plugin_dir;
+#if defined WITH_UDEV
+static gboolean  test_no_udev;
+#endif
 
 static const GOptionEntry test_entries[] = {
     {
@@ -239,6 +242,13 @@ static const GOptionEntry test_entries[] = {
         "Path to look for plugins",
         "[PATH]"
     },
+#if defined WITH_UDEV
+    {
+        "test-no-udev", 0, 0, G_OPTION_ARG_NONE, &test_no_udev,
+        "Run without udev support even if available",
+        NULL
+    },
+#endif
     { NULL }
 };
 
@@ -274,6 +284,14 @@ mm_context_get_test_plugin_dir (void)
     return test_plugin_dir ? test_plugin_dir : PLUGINDIR;
 }
 
+#if defined WITH_UDEV
+gboolean
+mm_context_get_test_no_udev (void)
+{
+    return test_no_udev;
+}
+#endif
+
 /*****************************************************************************/
 
 static void
@@ -345,5 +363,8 @@ mm_context_init (gint argc,
         g_warning ("error: --initial-kernel-events must be used only if --no-auto-scan is also used");
         exit (1);
     }
+    /* Force skipping autoscan if running test without udev */
+    if (test_no_udev)
+        no_auto_scan = TRUE;
 #endif
 }