[WCF] Disable CloseTest and OpenTest4 in CustomPeerResolverServiceTest.

These tests occasionally time out:

Test Case Failures:
1) MonoTests.System.ServiceModel.PeerResolvers.CustomPeerResolverServiceTest.CloseTest : System.TimeoutException : The operation has timed-out.
at System.ServiceModel.Channels.HttpRequestChannel+HttpChannelRequestAsyncResult.WaitEnd () [0x00000] in <filename unknown>:0
at System.ServiceModel.Channels.HttpRequestChannel.EndRequest (IAsyncResult result) [0x00000] in <filename unknown>:0
at System.ServiceModel.Channels.HttpRequestChannel.Request (System.ServiceModel.Channels.Message message, TimeSpan timeout) [0x00000] in <filename unknown>:0
at System.ServiceModel.MonoInternal.ClientRuntimeChannel.Request (System.ServiceModel.Channels.Message msg, TimeSpan timeout) [0x00000] in <filename unknown>:0
at System.ServiceModel.MonoInternal.ClientRuntimeChannel.Request (System.ServiceModel.Description.OperationDescription od, System.Object[] parameters) [0x00000] in <filename unknown>:0
at System.ServiceModel.MonoInternal.ClientRuntimeChannel.DoProcess (System.Reflection.MethodBase method, System.String operationName, System.Object[] parameters) [0x00000] in <filename unknown>:0
at System.ServiceModel.MonoInternal.ClientRuntimeChannel.Process (System.Reflection.MethodBase method, System.String operationName, System.Object[] parameters) [0x00000] in <filename unknown>:0

I.e. we're timing out waiting for the async wait handle here: https://github.com/mono/mono/blob/master/mcs/class/System.ServiceModel/System.ServiceModel.Channels/HttpRequestChannel.cs#L495

Since we have no current WCF maintainer and this is deep, deep within
WCF land and causes unstable builds on Jenkins, disable these tests
for now.

Bug: https://bugzilla.xamarin.com/show_bug.cgi?id=21069