lengthen notification test timeouts to address flakiness

also explicityly check for null objects to improve failure reports.

Bug: 34819666
Test: mmma -j20 platform_testing/tests/functional/notificationtests && adb install -r -g $OUT/data/app/NotificationFunctionalTests/NotificationFunctionalTests.apk && adb shell am instrument -w -e iterations 1 -e class com.android.notification.functional.NotificationInteractionTests#testDismissAll com.android.notification.functional/android.support.test.runner.AndroidJUnitRunner && runtest --path platform_testing/libraries/metrics-helper/tests
Change-Id: I946abc0f2c1b42f9b04c9c85beb6759381d1f8c3