Fix NetworkNotificationManagerTest

The testNotificationsShownAndCleared test was not doing anything
because the list of notification to show was always empty.

This patch fixes this issue and actually makes the test loop on
non-empty collections, and also fixes another ordering issue in
assertions themselves, hidden until now by the first issue.

Bug: 32561414
Test: runtest -x frameworks/base/tests/net/java/com/android/server/connectivity/NetworkNotificationManagerTest.java
Merged-In: I4837b1175d7c9133e9156e33acaa1e7e3341cc62
Change-Id: Ia30587bd68a87b83b62f57eeeb28fef7d95dbf81

(cherry picked from commit f8b804be)