Fix pipe tests by running as x86

These tests are failing with the latest build tools update which
switches tests to run as x64.  I've moved the tests back to x86
temporarily until they are fixed.
https://github.com/dotnet/corefx/issues/2818

Author: ericstj

src/System.IO.Pipes/tests/System.IO.Pipes.Tests.csproj

@@ -10,6 +10,8 @@
     <AssemblyName>System.IO.Pipes.Tests</AssemblyName>
     <ProjectGuid>{142469EC-D665-4FE2-845A-FDA69F9CC557}</ProjectGuid>
     <NuGetPackageImportStamp>d2615b94</NuGetPackageImportStamp>
+    <!-- Temporary workaround until tests are fixed on x64 -->
+    <TestArchitecture>x86</TestArchitecture>
   </PropertyGroup>
   <!-- Default configurations to help VS understand the configurations -->
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">