Bug 1589699 - disable parent-intercept specific WPT test when parent-intercept is not enabled. r=perry

I had authored the test as a mozilla-only WPT which means we can't trivially
run a check for whether parent intercept is enabled from within the test via
consulting with nsIServiceWorkerManager.

Differential Revision: https://phabricator.services.mozilla.com/D49787

--HG--
extra : moz-landing-system : lando

testing/web-platform/mozilla/meta/service-workers/update_completes_in_disconnected_global.https.html.ini

@@ -0,0 +1,3 @@
+[update_completes_in_disconnected_global.https.html]
+  disabled:
+    if not sw-e10s: https://bugzilla.mozilla.org/show_bug.cgi?id=1589699