sdk: Running dotnet sdk command from unit tests is not possible without using full path

Steps to reproduce

1. Create unit test project
2. Add following code into test

 var startInfo = new ProcessStartInfo
                    {
                        FileName = "dotnet",
                        Arguments = "--version",
                        UseShellExecute = false,
                        CreateNoWindow = true,
                        RedirectStandardError = true,
                        RedirectStandardOutput = true,
                        WorkingDirectory =  AppContext.BaseDirectory
                    };
                    var hostProcess = new Process() { StartInfo = startInfo };
                    hostProcess.ErrorDataReceived += (sender, dataArgs) => { Console.WriteLine(dataArgs.Data ?? string.Empty); };
                    hostProcess.OutputDataReceived += (sender, dataArgs) => { Console.WriteLine(dataArgs.Data ?? string.Empty); };
                    hostProcess.Start();
                    Console.WriteLine(hostProcess.MainModule.FileName);
                    hostProcess.BeginErrorReadLine();
                    hostProcess.BeginOutputReadLine();
                    hostProcess.WaitForExit();

1. dotnet test

Expected behavior

Current dotnet version gets displayed along with muxer dotnet.exe path.

Actual behavior

dotnet.exe from shared runtime directory is resolved and it throws an error.

C:\Users\pakrym\AppData\Local\Microsoft\dotnet\shared\Microsoft.NETCore.App\1.0.0-rc2-23929\dotnet.exe
Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly '--version' or one of its dependencies. The system cannot find the file specified.

Cause

When dotnet test runs it uses corehost from shared host directory to run xunit runner, and when test tries to start dotnet publish dotnet.exe gets resolved to one inside shared runtime folder because of rules below.

Resolution order:
    The directory from which the application loaded.
    The current directory for the parent process.
    The 32-bit Windows system directory. Use the GetSystemDirectory function to get the path of this directory.
    The 16-bit Windows system directory. There is no function that obtains the path of this directory, but it is searched. The name of this directory is System.
    The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
    The directories that are listed in the PATH environment variable. Note that this function does not search the per-application path specified by the App Paths registry key. To include this per-application path in the search sequence, use the ShellExecute function.

Environment data

dotnet --version output:

1.0.0-beta-002115