Alter test httplistener to use a new runspace rather than a job (#3966)

This improves the performance of the listener by not relying on a new
process starting up to run the listener. It improves the debugability
of tests by providing more direct access to the session executing
the listener. It also reverses the blocking nature of starting the
listener. By default, Start-HttpListener will no longer block, you need
to use -Foreground to have Start-HttpListener block. Lastly, create
a way to catch errors if the listener has a problem. If code in the
listener throws, it emits an error record.

test/powershell/Modules/Microsoft.PowerShell.Utility/WebCmdlets.Tests.ps1

@@ -146,11 +146,12 @@ function GetTestData
 Describe "Invoke-WebRequest tests" -Tags "Feature" {
 
     BeforeAll {
-        $null = Start-HttpListener -AsJob -Port 8080
+        $response = Start-HttpListener -Port 8080
     }
 
     AfterAll {
         $null = Stop-HttpListener -Port 8080
+        $response.PowerShell.Dispose()
     }
 
     # Validate the output of Invoke-WebRequest
@@ -576,11 +577,12 @@ Describe "Invoke-WebRequest tests" -Tags "Feature" {
 Describe "Invoke-RestMethod tests" -Tags "Feature" {
 
     BeforeAll {
-        $null = Start-HttpListener -AsJob -Port 8081
+        $response = Start-HttpListener -Port 8081
     }
 
     AfterAll {
         $null = Stop-HttpListener -Port 8081
+        $response.PowerShell.Dispose()
     }
 
     It "Invoke-RestMethod returns User-Agent" {

test/tools/Modules/HttpListener/HttpListener.psm1

@@ -37,7 +37,7 @@ Function Start-HTTPListener {
         [Int] $Port = 8080,
 
         [Parameter()]
-        [switch] $AsJob
+        [switch] $Foreground
         )
 
     Process {
@@ -214,19 +214,36 @@ Function Start-HTTPListener {
                     $response.Close()
                 }
             }
+            catch
+            {
+                $errormsg = $_ | convertto-json
+                Write-Error $errormsg
+            }
             finally
             {
                 $listener.Stop()
+                Write-Information "Listener is stopped" -InformationAction Continue
             }
         }
 
-        if ($AsJob)
-        {
-            Start-Job -ScriptBlock $script -ArgumentList $Port
-        }
-        else
+        if ($Foreground)
         {
             & $script -Port $Port
         }
+        else
+        {
+            $ps = [powershell]::Create()
+            $null = $ps.AddScript($script)
+            $null = $ps.AddParameter("port",$port)
+            $AsyncResponse = $ps.BeginInvoke()
+            # include the AsyncResponse in the return object
+            # it can be used to determine whether execution
+            # is still underway, and may be useful in debugging
+            # if something goes amiss
+            [pscustomobject]@{
+                PowerShell = $ps
+                AsyncResponse  = $AsyncResponse
+                }
+        }
     }
 }