Do not create another pinned task while entering PIP in the test

Another pinned task was created while AlwaysFocusablePipActivity was
started, which moved the original pinned task to fullscreen windowing
mode and the task was removed by sysui then. So, the
LaunchPipOnPipActivity was also removed and no longer visible.

This CL makes the AlwaysFocusablePipActivity into the same task as
LaunchPipOnPipActivity. The testing behavior is the same with phone.

Bug: 158111262
Test: atest testTranslucentActivityOnTopOfPinnedStack
Change-Id: I8915fe8365d13216c327cf860b53dde9a158e9da
1 file changed