Disable MetadataReader test against GitHub issue corefx/260

Commit migrated from https://github.com/dotnet/corefx/commit/f415d3355be85dd76fb55482bcffe7fc7eaec059

src/libraries/System.Reflection.Metadata/tests/Metadata/MetadataReaderTests.cs

@@ -2440,6 +2440,7 @@ public void Handles()
 
         [Fact]
         [OuterLoop]
+        [ActiveIssue(260)]
         public void CanReadFromSameMemoryMappedPEReaderInParallel()
         {
             // See http://roslyn.codeplex.com/workitem/299
@@ -2449,7 +2450,7 @@ public void CanReadFromSameMemoryMappedPEReaderInParallel()
             // on demand for callers on different threads.
             //
 
-            using (var stream = File.OpenRead(typeof(object).Assembly.Location))
+            /*using (var stream = File.OpenRead(typeof(object).Assembly.Location))
             {
                 Assert.True(stream.Length > StreamMemoryBlockProvider.MemoryMapThreshold);
 
@@ -2462,7 +2463,7 @@ public void CanReadFromSameMemoryMappedPEReaderInParallel()
                         Parallel.For(0, 4, _ => { peReader.GetMetadataReader(); });
                     }
                 }
-            }
+            }*/
         }
     }
 }