Update to SDK and MS.NET.Build.Extensions versions with latest fixes, fix RestoreDependency.proj to work when SdkLayoutDirectory isn't set

Author: dsplaisted

build/DependencyVersions.props

@@ -6,9 +6,9 @@
     <CLI_Roslyn_Version>2.3.0-beta2-61716-09</CLI_Roslyn_Version>
     <CLI_DiaSymNative_Version>1.6.0-beta2-25304</CLI_DiaSymNative_Version>
     <CLI_FSharp_Version>4.2.0-rc-170602-0</CLI_FSharp_Version>
-    <CLI_NETSDK_Version>2.0.0-preview2-20170606-4</CLI_NETSDK_Version>
+    <CLI_NETSDK_Version>2.0.0-preview2-20170608-2</CLI_NETSDK_Version>
     <CLI_NuGet_Version>4.3.0-preview3-4146</CLI_NuGet_Version>
-    <CLI_MSBuildExtensions_Version>2.0.0-preview2-20170606-4</CLI_MSBuildExtensions_Version>
+    <CLI_MSBuildExtensions_Version>2.0.0-preview2-20170608-2</CLI_MSBuildExtensions_Version>
     <CLI_NETStandardLibraryNETFrameworkVersion>2.0.0-preview2-25331-02</CLI_NETStandardLibraryNETFrameworkVersion>
     <CLI_WEBSDK_Version>2.0.0-rel-20170518-512</CLI_WEBSDK_Version>
     <CLI_TestPlatform_Version>15.3.0-preview-20170601-03</CLI_TestPlatform_Version>

build/RestoreDependency.proj

@@ -1,4 +1,4 @@
-<Project ToolsVersion="15.0" DefaultTargets="CopySdkToOutput">
+<Project ToolsVersion="15.0" DefaultTargets="EnsureDependencyRestored;CopySdkToOutput">
   <!-- workaround for https://github.com/Microsoft/msbuild/issues/885 -->
   <!-- renaming the property because the original property is a global property and therefore
        cannot be redefined at runtime. -->