[msbuild] Fix MSBuild tests to build using Xcode 9.

[rolfbjarne]

Set the min deployment target to 7.0 for a test to make sure ibtool doesn't
complain, and fix the list of expected bundle resources by adding Assets.car
to the list.

Fixes the following failures:

1. Xamarin.iOS.Tasks.TargetTests.BuildExecutable : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

2. Xamarin.iOS.Tasks.TargetTests.BundleResources : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

3. Xamarin.iOS.Tasks.TargetTests.CleanExecutable : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

4. Xamarin.iOS.Tasks.TargetTests.CopyContentToBundle : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

5. Xamarin.iOS.Tasks.TargetTests.Disappearing_Bundle_Resource : [appkit] Add NSImage lazy initialization #2

   Expected: True
   But was: False

6. Xamarin.iOS.Tasks.TargetTests.Disappearing_Content : [appkit] Add NSImage lazy initialization #2

   Expected: True
   But was: False

7. Xamarin.iOS.Tasks.TargetTests.OptimizePngs_DefaultValue : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

8. Xamarin.iOS.Tasks.TargetTests.OptimizePngs_False : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

9. Xamarin.iOS.Tasks.TargetTests.OptimizePngs_True : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
   

   Expected: 0
   But was: 2

10. Xamarin.iOS.Tasks.TargetTests.RebuildExecutable_NoModifications : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
    

    Expected: 0
    But was: 2

11. Xamarin.iOS.Tasks.TargetTests.RebuildExecutable_TouchLibraryDll : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
    

    Expected: 0
    But was: 2

12. Xamarin.iOS.Tasks.TargetTests.UnpackLibraryResources_ExecutableProject : #RunTarget-ErrorCount

    ibtool exited with code 1
    Compiling IB documents for earlier than iOS 7 is no longer supported.
    

    Expected: 0
    But was: 2

[monojenkins]

Build failure