[Tests] Make the CoreBluetooth tests more reliable. (#7115)

Tests were failing because the manager was getting dispose and the
delegate was not. We ran into the failure because there was a device
close to the lab with the UUID that was being used.

The change uses a even more common UUID (heart monitor), which should
increase the chances to pick up a device and re-orgs the disposal of the
manager and the delegate.

This was confirmed with a BLE device, watchOS does not like us to try
and access it as a bluetooth device and is 'hacky'.

Fixes: https://github.com/xamarin/xamarin-macios/issues/7108

tests/monotouch-test/CoreBluetooth/CentralManagerTest.cs

@@ -77,13 +77,16 @@ namespace MonoTouchFixtures.CoreBluetooth {
 
 		CBCentralManager mgr;
 		ManagerDelegate mgrDelegate;
+		CBUUID heartRateMonitorUUID; 
 
 		[SetUp]
 		public void SetUp ()
 		{
 			// iOS 13 and friends require bluetooth permission
 			if (TestRuntime.CheckXcodeVersion (11, 0))
-			    TestRuntime.CheckBluetoothPermission ();
+				TestRuntime.CheckBluetoothPermission ();
+			//known UUID for a heart monitor, more common, we want to find something and make sure we do not crash
+			heartRateMonitorUUID = CBUUID.FromPartial (0x180D);
 			// Required API is available in macOS 10.8, but it doesn't work (hangs in 10.8-10.9, randomly crashes in 10.10) on the bots.
 			TestRuntime.AssertSystemVersion (PlatformName.MacOSX, 10, 11, throwIfOtherPlatform: false);
 			var e = new AutoResetEvent (false);
@@ -94,7 +97,8 @@ namespace MonoTouchFixtures.CoreBluetooth {
 		[TearDown]
 		public void TearDown ()
 		{
-			// should dispose the delegate
+			heartRateMonitorUUID?.Dispose ();
+			mgrDelegate?.Dispose ();  // make sure that our delegate does not get messages after the mgr was disposed
 			mgr?.Dispose ();
 		}
 			
@@ -110,7 +114,6 @@ namespace MonoTouchFixtures.CoreBluetooth {
 			Assert.NotNull (mgr.Delegate, "Delegate");
 		}
 
-		[Ignore ("https://github.com/xamarin/xamarin-macios/issues/7108")]
 		[Test, Timeout (5000)]
 		public void ScanForPeripherals ()
 		{
@@ -124,7 +127,6 @@ namespace MonoTouchFixtures.CoreBluetooth {
 		}
 
 #if !XAMCORE_3_0
-		[Ignore ("https://github.com/xamarin/xamarin-macios/issues/7108")]
 		[Test, Timeout (5000)]
 		public void RetrievePeripherals ()
 		{
@@ -136,12 +138,12 @@ namespace MonoTouchFixtures.CoreBluetooth {
 				Assert.Inconclusive ("Bluetooth is off and therefore the test cannot be ran. State == {0}.", mgr.State);
 
 			if (TestRuntime.CheckXcodeVersion (7, 0)) {
-				using (var uuid = new NSUuid ("B9401000-F5F8-466E-AFF9-25556B57FE6D"))
+				// ToString in a CBUUID with true returns the full uuid which can be used to create a NSUuid
+				using (var uuid = new NSUuid (heartRateMonitorUUID.ToString (true)))
 					mgr.RetrievePeripheralsWithIdentifiers (uuid);
 			} else {
 				// that API was deprecated in 7.0 and removed from 9.0
-				using (var uuid = CBUUID.FromString ("B9401000-F5F8-466E-AFF9-25556B57FE6D"))
+				mgr.RetrievePeripherals (heartRateMonitorUUID);
-					mgr.RetrievePeripherals (uuid);
 			}
 		}
 #endif // !XAMCORE_3_0