Add Start-TestSleep to avoid waiting during playback mode (#1285)

powershell/resources/psruntime/BuildTime/Cmdlets/ExportTestStub.cs

@@ -56,6 +56,31 @@ namespace Microsoft.Rest.ClientRuntime.PowerShell
         return -join ((48..57) + (97..122) | Get-Random -Count $len | % {[char]$_})
     }
 }
+function Start-TestSleep {
+    [CmdletBinding(DefaultParameterSetName = 'SleepBySeconds')]
+    param(
+        [parameter(Mandatory = $true, Position = 0, ParameterSetName = 'SleepBySeconds')]
+        [ValidateRange(0.0, 2147483.0)]
+        [double] $Seconds,
+
+        [parameter(Mandatory = $true, ParameterSetName = 'SleepByMilliseconds')]
+        [ValidateRange('NonNegative')]
+        [Alias('ms')]
+        [int] $Milliseconds
+    )
+
+    if ($TestMode -ne 'playback') {
+        switch ($PSCmdlet.ParameterSetName) {
+            'SleepBySeconds' {
+                Start-Sleep -Seconds $Seconds
+            }
+            'SleepByMilliseconds' {
+                Start-Sleep -Milliseconds $Milliseconds
+            }
+        }
+    }
+}
+
 $env = @{}
 if ($UsePreviousConfigForRecord) {
     $previousEnv = Get-Content (Join-Path $PSScriptRoot 'env.json') | ConvertFrom-Json