refactor(wakeup): move exit to function, use constants

- move graceful exit to function to DRY code
- use constant for wol module name

wakeup.ps1

@@ -32,8 +32,14 @@ function exitError($errMessage, $PSItem, $exitCode = 1)
     Exit $exitCode
 }
 
-$wolModuleName = "wol-magicPacket"
-$wolDatabase = "WOLDatabase.xml"
+function exitGracefully()
+{
+    Write-Host -ForegroundColor Green "`r`nFinished.`r`n"
+    Exit 0
+}
+
+# constants
+Set-Variable -Name wolModuleName -Value "wol-magicPacket" -Option Constant
 
 # exit on error if Send-MagicPacket module is not loaded
 if (!(Get-Module -Name $wolModuleName))