(MODULES-10653) Failed to upgrade agent using puppet task

Before this commit, when trying to run the
`puppet_agent::install_powershell` task, with a specific version as
parameter, it was failing with below error message:
Error: Timed out waiting for status response from <node_name>

On the node, both `puppet agent` and `pxp-agent` services got stopped
and the event log viewer showed:
Application or service 'task_wrapper' could not be shut down.

Due to Windows agents becoming unresponsive when running this task and
as per MODULES-10633 discussions, the `puppet_agent::install_poweshell`
task should not be used for upgrading Puppet Agents. This Puppet Agent
module task will now stop immediately and output a message if the Puppet
Agent is already installed on the node.

Author: luchihoratiu

tasks/install_powershell.ps1

@@ -34,6 +34,10 @@ function Test-PuppetInstalled {
   }
 }
 
+if (Test-PuppetInstalled) {
+  Write-Error "Puppet Agent is already installed on this node. Nothing to do."
+}
+
 if ($version) {
     if ($version -eq "latest") {
       $msi_name = "puppet-agent-${arch}-latest.msi"
@@ -42,11 +46,6 @@ if ($version) {
     }
 }
 else {
-    if (Test-PuppetInstalled) {
-      Write-Output "Puppet Agent detected and no version specified. Nothing to do."
-      Exit
-    }
-
     $msi_name = "puppet-agent-${arch}-latest.msi"
 }