Gather test diag logging to track down nuget issue

We're seeing NU3003 for packages that when downloaded manually, don't show an issue. Per NuGet team, this means an exception is thrown and collecting verbosity information should help.

I believe I've mostly seen this on windows so let's enable for windows and just keep rerunning until we hit it.

Author: marcpopMSFT

build/RunTestsOnHelix.cmd

@@ -23,6 +23,7 @@ mkdir %TestExecutionDirectory%
 REM https://stackoverflow.com/a/7487697/294804
 robocopy %HELIX_CORRELATION_PAYLOAD%\t\TestExecutionDirectoryFiles %TestExecutionDirectory% /s /nfl /ndl /njh /njs /np
 
+set Verbosity=diagnostic
 set DOTNET_SDK_TEST_EXECUTION_DIRECTORY=%TestExecutionDirectory%
 set DOTNET_SDK_TEST_MSBUILDSDKRESOLVER_FOLDER=%HELIX_CORRELATION_PAYLOAD%\r
 set DOTNET_SDK_TEST_ASSETS_DIRECTORY=%TestExecutionDirectory%\TestAssets