Wait after pressing home

Fix CtsAppOpTestCases flakiness in Android 12L GAS devices.

ForegroundModeAndActiveTest.kt often fails because the
AppOpsForegroundControlActivity activity is started
before the shell command to go to home
be processed by the framework.

It causes the expectations get misaligned
and the test fails with timeout.

(Cherry-pick) Original Commit:
Test:  android-cts-12.1r10/android-cts/tools/cts-tradefed
run commandAndExit cts --include-filter 'CtsAppOpsTestCases
android.app.appops.cts.ForegroundModeAndActiveTest' (50x)

Bug: 229827129
Bug: 353758396

(cherry picked from commit bc05a61ea6b8895a316c8047e467e54f6c2a87f7)
Merged-In: I63de4f938284e1ca4a90d7bba5541a4143964545
Change-Id: I1f40fd3b4905c6da93a7af6f183c3a5d34f465c6