Race around TestResults directory creation

[pakrym]

We need to add { recursive: true } parameter to https://github.com/Azure/autorest.testserver/blob/master/legacy/app.js#L59

Error: EEXIST: file already exists, mkdir 'D:\a\1\s\autorest.csharp\node_modules\@microsoft.azure\autorest.testserver\TestResults'
    at Object.mkdirSync (fs.js:934:3)
    at Object.<anonymous> (D:\a\1\s\autorest.csharp\node_modules\@microsoft.azure\autorest.testserver\legacy\app.js:59:6)
    at Module._compile (internal/modules/cjs/loader.js:1118:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1138:10)
    at Module.load (internal/modules/cjs/loader.js:982:32)
    at Function.Module._load (internal/modules/cjs/loader.js:875:14)
    at Module.require (internal/modules/cjs/loader.js:1022:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (D:\a\1\s\autorest.csharp\node_modules\@microsoft.azure\autorest.testserver\legacy\startup\www.js:7:11)
    at Module._compile (internal/modules/cjs/loader.js:1118:30) {
  errno: -4075,
  syscall: 'mkdir',
  code: 'EEXIST',
  path: 'D:\\a\\1\\s\\autorest.csharp\\node_modules\\@microsoft.azure\\autorest.testserver\\TestResults'
}