Wait for launcher is shown after calling pressHome

In current code, the test will call pressHome before show
network notification but it does not verify the home screen
is shown. The test might be failed due to the notification
shade is still opened. Thus adding an assertion to verify
the launcher is shown.

Bug: 255643296
Test: FrameworksNetTest:NetworkNotificationManagerTest
Change-Id: Iee3476a26030b9ba72994dee624e0e6974c9369f
2 files changed