Fix #testNormalActivityCanNotSetActivityType flakiness

Home activity is always visible and resumed in freefrom display.
When another home type activity was resumed, the default home
activity was paused. The default home activity was then resumed
and brought home task to front when the test home type activity
finished. Sometimes, it also resulted in the next test activity
stopped and caused the test flaky.

Bug: 189135702
Test: atest StartActivityTests
Change-Id: Ic4d5a6c43cebd5715c731f2c25356e72bf440a10