Reduce unnecessary output when running tests

[RikkiGibson]

When I use the Run Tests in Context in VS Code I get a lot of output like this:

Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.NullableReferenceTypesTests.UnconstrainedTypeParameter_03:
    Outcome: Passed
    
Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.NullableReferenceTypesTests.Operator_06:
    Outcome: Passed
    
Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.NullableReferenceTypesTests.WarnInsideTupleLiteral:
    Outcome: Passed
    
Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.NullableReferenceTypesTests.SuppressNullableWarning_Out:
    Outcome: Passed
    
Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.NullableReferenceTypesTests.NotNull_EnforceInMethodBody_Warn_TransientAssignmentOkay:
    Outcome: Passed
...

It doesn't seem necessary to include this, we could instead just give the count of tests that were run and include details for any failing or skipped tests.

It's possible that this could be fixed in https://github.com/omnisharp/omnisharp-roslyn/blob/master/src/OmniSharp.DotNetTest/VSTestManager.cs