Fix flake in ManageStandardPermissionsTest

Bug: 269730384

This CL fixes two issue
1) additionalPermissionSummaryGetUpdateWhenDefinerGetsUninstalled
   sometimes flaky because when the app is not yet uninstalled, the
   additional permission preference. And when it's tryign to find the
   app count, it failed because the app is uninstalled. Changed to
   return 0 when app count is not available.
2) We might have to look more into this but sometimes uninstallApp()
   doesn't correctly uninstall the app. After calling uninstallApp() in
   @After, when running the test, it's still showing. I added an
   install/uninstall in @Before as well. This is a bit ugly but when
   testing it, the tests pass consistently

Test: build
Change-Id: I7ab35b2c55448cbc5f49c2cf75e78ca7d06058b5