[tests][mtouch] Adjust tests to cope with Xcode 9. Fixes #57601.

[rolfbjarne]

Fixes:

1. Failed : Xamarin.MTouch.MT0091(tvOS,"tvOS")

    The error 'MT0091: This version of Xamarin.iOS requires the tvOS 11.0 SDK (shipped with Xcode 9.0). Either upgrade Xcode to get the required header files or set the managed linker behaviour to Link Framework SDKs Only (to try to avoid the new APIs).' was not found in the output:
    Message #1 did not match:
        actual:   'This version of Xamarin.iOS requires the tvOS 11.0 SDK (shipped with Xcode 9). Either upgrade Xcode to get the required header files or set the managed linker behaviour to Link Framework SDKs Only (to try to avoid the new APIs).'
        expected: 'This version of Xamarin.iOS requires the tvOS 11.0 SDK (shipped with Xcode 9.0). Either upgrade Xcode to get the required header files or set the managed linker behaviour to Link Framework SDKs Only (to try to avoid the new APIs).'

2. Failed : Xamarin.MTouch.MT0091(iOS,"iOS")

    The error 'MT0091: This version of Xamarin.iOS requires the iOS 11.0 SDK (shipped with Xcode 9.0). Either upgrade Xcode to get the required header files or set the managed linker behaviour to Link Framework SDKs Only (to try to avoid the new APIs).' was not found in the output:
    Message #1 did not match:
        actual:   'This version of Xamarin.iOS requires the iOS 11.0 SDK (shipped with Xcode 9). Either upgrade Xcode to get the required header files or set the managed linker behaviour to Link Framework SDKs Only (to try to avoid the new APIs).'
        expected: 'This version of Xamarin.iOS requires the iOS 11.0 SDK (shipped with Xcode 9.0). Either upgrade Xcode to get the required header files or set the managed linker behaviour to Link Framework SDKs Only (to try to avoid the new APIs).'

3. Failed : Xamarin.Registrar.NoWarnings

    no warnings
    Expected: not String matching "warning:"
    But was:  "/Users/builder/jenkins/workspace/xamarin-macios-pr-builder/tests/mtouch/bin/Debug/tmp-test-dir/Xamarin.MTouchTool.CreateTemporaryDirectory298/mtouch-test-cache/registrar.m:32468:17: warning: method 'paymentAuthorizationViewController:didAuthorizePayment:handler:' in protocol 'PKPaymentAuthorizationViewControllerDelegate' not implemented [-Wprotocol]"

https://bugzilla.xamarin.com/show_bug.cgi?id=57601

[monojenkins]

Build failure

[rolfbjarne]

build

[monojenkins]

Build success