Remove duplicate invocation and enable webserver

For no obvious reason, the configure proxy script is invoked twice. Also
it would be nice to explicitly enable the webserver so the generated
image is usable after boot.

tests/install/openqa_webui.pm

@@ -26,10 +26,11 @@ sub install_from_pkgs {
     assert_script_run "/usr/share/openqa/script/configure-web-proxy $proxy_args";
     if (check_var('OPENQA_WEB_PROXY', 'nginx')) {
         assert_script_run 'systemctl disable --now apache2';
+        assert_script_run 'systemctl enable nginx';
         assert_script_run 'systemctl restart nginx';
     }
     else {
-        assert_script_run '/usr/share/openqa/script/configure-web-proxy';
+        assert_script_run 'systemctl enable apache2';
         assert_script_run 'systemctl restart apache2';
     }
     assert_script_run($_) foreach (split /\n/, <<~'EOF');