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.

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