Disable re-setting the renderPipeline for a graphic if it is already set.

Add "/Scenes" to the hd pipe test scenes search, to ignore the playmod test scene.

Tests/GraphicsTests/Framework/Editor/TestFramework.cs

             {
                 get
                 {
-                    return GetScenesForPipeline("HDRenderPipeline");
+                    return GetScenesForPipeline("HDRenderPipeline/Scenes");
                 }
             }
 

Tests/GraphicsTests/Framework/SetupSceneForRenderPipelineTest.cs

-using UnityEngine.Rendering;
+using UnityEngine.Rendering;
 
 namespace UnityEngine.Experimental.Rendering
 {
 		public void Setup()
 		{
 			m_OriginalAsset = GraphicsSettings.renderPipelineAsset;
-			GraphicsSettings.renderPipelineAsset = renderPipeline;
+            if (m_OriginalAsset != renderPipeline) GraphicsSettings.renderPipelineAsset = renderPipeline;
-			GraphicsSettings.renderPipelineAsset = m_OriginalAsset;
+			if ( GraphicsSettings.renderPipelineAsset != m_OriginalAsset ) GraphicsSettings.renderPipelineAsset = m_OriginalAsset;
 		}
 	}
 }