Make TimeZone tests more reliable.

[dellis1972]

The Timezone tests have been very unreliable recently. We speculate that this is down to the emulator not
running as fast as it used to on the CI system.

This PR attempts to make these tests more reliable.
Firstly we will make use of the NonParallelizable attribute to ensure that the tests run in sequence. This
is to stop them tripping over each other when setting the timezone. Next up we will add a Retry attribute
to at least re run a test once if it fails. This might help if the emulator is running slowly.

Next we introduce the following code both before and after the test.

RunAdbCommand ($"shell am force-stop --user all {proj.PackageName}");
RunAdbCommand ($"shell am kill --user all {proj.PackageName}");

These commands will force the application to stop, and face any background tasks the application has
to stop as well. This is the best way we could fine to completely kill the application. While we were
expecting the TimeZoneChanged notification to fire if the app was already running, it turns out that
when setting the date time via adb that broadcast does NOT get fired. It only fires when the timezone
is changed via the Settings screen. So killing the application completely and forcing a restart is the best
option. We should investigate to see if we can script the timezone change via the UI so we can test the
broadcast, but that should be done in a separate PR.