Adds support to restore original config after using old PS module

Fixes #65

lib/core/icingaagent/misc/Reset-IcingaAgentConfigFile.psm1

@@ -0,0 +1,30 @@
+<#
+.SYNOPSIS
+   Checks for old configurations provided by the old PowerShell module
+   and restores the original configuration file
+.DESCRIPTION
+   Restores the original Icinga 2 configuration by replacing the existing
+   configuration created by the old PowerShell module with the plain one
+   from the Icinga 2 backup file
+.FUNCTIONALITY
+   Restores original Icinga 2 configuration icinga2.conf
+.EXAMPLE
+   PS>Reset-IcingaAgentConfigFile;
+.LINK
+   https://github.com/Icinga/icinga-powershell-framework
+#>
+
+function Reset-IcingaAgentConfigFile()
+{
+    $ConfigDir       = Get-IcingaAgentConfigDirectory;
+    $OldConfig       = Join-Path -Path $ConfigDir -ChildPath 'icinga2.conf';
+    $OldConfigBackup = Join-Path -Path $ConfigDir -ChildPath 'icinga2.conf.old.module';
+    $OriginalConfig  = Join-Path -Path $ConfigDir -ChildPath 'icinga2.confdirector.bak';
+
+    if ((Test-Path $OriginalConfig)) {
+        Write-Host 'Found icinga2.conf backup file created by old PowerShell module. Restoring original configuration';
+
+        Move-Item -Path $OldConfig      -Destination $OldConfigBackup;
+        Move-Item -Path $OriginalConfig -Destination $OldConfig;
+    }
+}

lib/core/icingaagent/misc/Start-IcingaAgentInstallWizard.psm1

@@ -474,6 +474,7 @@ function Start-IcingaAgentInstallWizard()
 
     if ($RunInstaller) {
         if ((Install-IcingaAgent -Version $AgentVersion -Source $PackageSource -AllowUpdates $AllowVersionChanges) -Or $Reconfigure) {
+            Reset-IcingaAgentConfigFile;
             Move-IcingaAgentDefaultConfig;
             Set-IcingaAgentNodeName -Hostname $Hostname;
             Set-IcingaAgentServiceUser -User $ServiceUser -Password $ServicePass -SetPermission | Out-Null;