Fixed a few issues around bootstrapping

- Work aronud coreconsole issue in the bootstrap.cmd
- Use msbuild 14 roslyn csc until we have it
- Remove quoting args when building project refs, it wasn't working
- Fixed logic that launched exe's directly

src/Microsoft.DotNet.Cli.Utils/Command.cs

@@ -77,9 +77,9 @@ namespace Microsoft.DotNet.Cli.Utils
             if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
                 var extension = Path.GetExtension(executable);
-                if (!string.IsNullOrEmpty(executable))
+                if (!string.IsNullOrEmpty(extension))
                 {
-                    return string.Equals(executable, ".exe", StringComparison.Ordinal);
+                    return !string.Equals(extension, ".exe", StringComparison.Ordinal);
                 }
                 else if (executable.Contains(Path.DirectorySeparatorChar))
                 {