Skip telemetry_notification_api test due to bug 1336755

Temporarily skip the nova notification test due to the frequency
of timeouts in the gate, pending a fix for bug LP #1336755.

Related-Bug: 1336755

Change-Id: Ie0eef11998f4647a3e187b357630d9531a6cf1e8
Merge "Skip telemetry_notification_api test due to bug 1336755"