Don't fail if SaferPolicy API is not available on Win10 IoT or NanoServer (#7075)

* don't fail if SaferApi is not available
* fix install-powershellremoting to work on Windows PowerShell 5.1

src/powershell-native/Install-PowerShellRemoting.ps1

@@ -124,7 +124,7 @@ function Install-PluginEndpoint {
     #                    #
     ######################
 
-    if ($PsCmdlet.ParameterSetName -eq "ByPath")
+    if ($PowerShellHome -ne $null)
     {
         $targetPsHome = $PowerShellHome
         $targetPsVersion = & "$targetPsHome\pwsh" -NoProfile -Command '$PSVersionTable.PSVersion.ToString()'
@@ -135,6 +135,7 @@ function Install-PluginEndpoint {
         $targetPsHome = $PSHOME
         $targetPsVersion = $PSVersionTable.PSVersion.ToString()
     }
+    Write-Verbose "PowerShellHome: $targetPsHome" -Verbose
 
     # For default, not tied to the specific version endpoint, we apply
     # only first number in the PSVersion string to the endpoint name.
@@ -163,7 +164,16 @@ function Install-PluginEndpoint {
         return
     }
 
-    $pluginBasePath = Join-Path ([System.Environment]::GetFolderPath([System.Environment+SpecialFolder]::Windows) + "\System32\PowerShell") $targetPsVersion
+    if ($PSVersionTable.PSVersion -lt "6.0")
+    {
+        # This script is primarily used from Windows PowerShell for Win10 IoT and NanoServer to setup PSCore6 remoting endpoint
+        # so it's ok to hardcode to 'C:\Windows' for those systems
+        $pluginBasePath = Join-Path "C:\Windows\System32\PowerShell" $targetPsVersion
+    }
+    else
+    {
+        $pluginBasePath = Join-Path ([System.Environment]::GetFolderPath([System.Environment+SpecialFolder]::Windows) + "\System32\PowerShell") $targetPsVersion
+    }
 
     $resolvedPluginAbsolutePath = ""
     if (! (Test-Path $pluginBasePath))