Disable testNetworkPassedDoesNotRollback

This is an effort to fix flaky StagedRollbackTest.

My local tests show that the crash has something to do with repeatedly
turn on/off network connection for each test. Several things are done
below to reduce the flakiness:

1. Disable testNetworkPassedDoesNotRollback
   It sometimes takes more than 5 minutes for the device to be back
   online after turning on the network connection during the test. This
   test contributes a lot to the flakiness. Let's disable it for now so
   other tests can keep running.
2. Rewrite testNetworkFailedRollback so we only turn on/off network
   connection when necessary in the hope to reduce the WifiHandlerThread
   crash. The change works pretty well for my local tests which run over
   40 loops without a single failure.

Bug: 143514090
Test: atest StagedRollbackTest
Change-Id: I9aec5eafdd3368ef76517e3b8500970e60d07487