Fix pip window visibility assertions

1) Fix `Could not find: PipApp`, the test previously used the launcher name, instead of the window name for assertion

2) The command previously missed a `verify` call to actually execute the assertion

Bug: 186115871
Bug: 186445782
Test: atest FlickerTests WMShellFlickerTests
Change-Id: Ie9274e273bcda2be24491705cd28d7dc0d5ea5db