SqlServerDsc: Fixes the timing issue with SqlServiceAccount (#1019)

- Changes to SqlServerDsc
  - Now the helper function Restart-SqlService, after restarting the SQL Server
    service, does not return until it can connect to the SQL Server instance, and
    the instance returns status 'Online' (issue #1008).
    If it fails to connect within the timeout period (defaults to 120 seconds) it
    throws an error.
- Changes to SqlServiceAccount
  - The timing issue that the resource returned before SQL Server service was
    actually restarted has been solved by a change in the helper function
    Restart-SqlService (issue #1008).
    Now Restart-SqlService waits for the instance to return status 'Online' or
    throws an error saying it failed to connect within the timeout period.

CHANGELOG.md

@@ -41,6 +41,11 @@
   - Updated the security token for AppVeyor status badge in README.md. When we
     renamed the repository the security token was changed
     ([issue #1012](https://github.com/PowerShell/SqlServerDsc/issues/1012)).
+  - Now the helper function Restart-SqlService, after restarting the SQL Server
+    service, does not return until it can connect to the SQL Server instance, and
+    the instance returns status 'Online' ([issue #1008](https://github.com/PowerShell/SqlServerDsc/issues/1008)).
+    If it fails to connect within the timeout period (defaults to 120 seconds) it
+    throws an error.
   - Fixed typo in comment-base help for helper function Test-AvailabilityReplicaSeedingModeAutomatic.
   - Style cleanup in helper function tests.
 - Changes to SqlAG
@@ -127,6 +132,11 @@
     name is correctly returned as a string ([issue #982](https://github.com/PowerShell/SqlServerDsc/issues/982)).
   - Added integration tests ([issue #980](https://github.com/PowerShell/SqlServerDsc/issues/980)).
   - Minor code style cleanup.
+  - The timing issue that the resource returned before SQL Server service was
+    actually restarted has been solved by a change in the helper function
+    Restart-SqlService ([issue #1008](https://github.com/PowerShell/SqlServerDsc/issues/1008)).
+    Now Restart-SqlService waits for the instance to return status 'Online' or
+    throws an error saying it failed to connect within the timeout period.
 - Changes to SqlSetup
   - Added parameter `ASServerMode` to support installing Analysis Services in
     Multidimensional mode, Tabular mode and PowerPivot mode

SqlServerDscHelper.psm1

@@ -842,6 +842,34 @@ function Restart-SqlService
             $_ | Start-Service
         }
     }
+
+    Write-Verbose -Message ($script:localizedData.WaitingInstanceTimeout -f $SQLServer, $SQLInstanceName, $Timeout) -Verbose
+
+    $connectTimer = [System.Diagnostics.StopWatch]::StartNew()
+
+    do
+    {
+        # This call, if it fails, will take between ~9-10 seconds to return.
+        $testConnectionServerObject = Connect-SQL -SQLServer $SQLServer -SQLInstanceName $SQLInstanceName -ErrorAction SilentlyContinue
+        if ($testConnectionServerObject -and $testConnectionServerObject.Status -ne 'Online')
+        {
+            # Waiting 2 seconds to not hammer the SQL Server instance.
+            Start-Sleep -Seconds 2
+        }
+        else
+        {
+            break
+        }
+    } until ($connectTimer.Elapsed.Seconds -ge $Timeout)
+
+    $connectTimer.Stop()
+
+    # Was the timeout period reach before able to connect to the SQL Server instance?
+    if (-not $testConnectionServerObject -or $testConnectionServerObject.Status -ne 'Online')
+    {
+        $errorMessage = $script:localizedData.FailedToConnectToInstanceTimeout -f $SQLServer, $SQLInstanceName, $Timeout
+        New-InvalidOperationException -Message $errorMessage
+    }
 }
 
 <#