Make tests robust without depending on the order of attributes

[mikkelbu]

Relates to #2326 (perhaps even closes the issue?)

[mikkelbu]

The test SetWaitHandle_Enqueue_Asynchronous failed in the .NET3.5 build.

2018-05-16T22:31:57.2588548Z 1-1) Failed : NUnit.Framework.Internal.Execution.EventQueueTests+SetWaitHandle_Enqueue_AsynchronousTest.SetWaitHandle_Enqueue_Asynchronous
2018-05-16T22:31:57.2589299Z   Expected: True
2018-05-16T22:31:57.2589582Z   But was:  False
2018-05-16T22:31:57.2589989Z    at NUnit.Framework.Internal.Execution.EventQueueTests.SetWaitHandle_Enqueue_AsynchronousTest.Consumer() in D:\a\1\s\src\NUnitFramework\tests\Internal\EventQueueTests.cs:line 196
2018-05-16T22:31:57.2590640Z    at NUnit.Framework.Internal.Execution.EventQueueTests.ProducerConsumerTest.ConsumerThreadWrapper() in D:\a\1\s\src\NUnitFramework\tests\Internal\EventQueueTests.cs:line 316
2018-05-16T22:31:57.2592618Z 
2018-05-16T22:31:57.2593370Z 1-2) Failed : NUnit.Framework.Internal.Execution.EventQueueTests+SetWaitHandle_Enqueue_AsynchronousTest.SetWaitHandle_Enqueue_Asynchronous
2018-05-16T22:31:57.2593848Z   Expected: null
2018-05-16T22:31:57.2594045Z   But was:  <NUnit.Framework.AssertionException:   Expected: True
2018-05-16T22:31:57.2594279Z   But was:  False
2018-05-16T22:31:57.2594380Z 
2018-05-16T22:31:57.2594657Z    at NUnit.Framework.Assert.ReportFailure(String message) in D:\a\1\s\src\NUnitFramework\framework\Assert.cs:line 394
2018-05-16T22:31:57.2595008Z    at NUnit.Framework.Assert.That[TActual](TActual actual, IResolveConstraint expression, String message, Object[] args) in D:\a\1\s\src\NUnitFramework\framework\Assert.That.cs:line 246
2018-05-16T22:31:57.2595441Z    at NUnit.Framework.Internal.Execution.EventQueueTests.SetWaitHandle_Enqueue_AsynchronousTest.Consumer() in D:\a\1\s\src\NUnitFramework\tests\Internal\EventQueueTests.cs:line 196
2018-05-16T22:31:57.2595972Z    at NUnit.Framework.Internal.Execution.EventQueueTests.ProducerConsumerTest.ConsumerThreadWrapper() in D:\a\1\s\src\NUnitFramework\tests\Internal\EventQueueTests.cs:line 316>
2018-05-16T22:31:57.2596393Z    at NUnit.Framework.Internal.Execution.EventQueueTests.ProducerConsumerTest.RunProducerConsumer() in D:\a\1\s\src\NUnitFramework\tests\Internal\EventQueueTests.cs:line 304
2018-05-16T22:31:57.2596895Z    at NUnit.Framework.Internal.Execution.EventQueueTests.SetWaitHandle_Enqueue_AsynchronousTest.SetWaitHandle_Enqueue_Asynchronous() in D:\a\1\s\src\NUnitFramework\tests\Internal\EventQueueTests.cs:line 181

[jnm2]

LGTM