Allow reinstallation of MSI packages (#3958)

Make the necessary changes to the WiX XML to allow the generated MSI
installers to be reinstalled.

changes/reinstall-msi

@@ -0,0 +1 @@
+* Allow MSI packages generated by `fleetctl package` to reinstall on Windows without uninstall.

orbit/pkg/packaging/windows_templates.go

@@ -8,7 +8,7 @@ var windowsWixTemplate = template.Must(template.New("").Option("missingkey=error
 	`<?xml version="1.0" encoding="UTF-8"?>
 <Wix xmlns="http://schemas.microsoft.com/wix/2006/wi" xmlns:util="http://schemas.microsoft.com/wix/UtilExtension">
   <Product
-    Id="C2C2437D-0562-465E-A0BB-2C4484025BD6"
+    Id="*"
     Name="Fleet osquery"
     Language="1033"
     Version="{{.Version}}"
@@ -16,7 +16,6 @@ var windowsWixTemplate = template.Must(template.New("").Option("missingkey=error
     UpgradeCode="B681CB20-107E-428A-9B14-2D3C1AFED244" >
 
     <Package
-      Id="*"
       Keywords='Fleet osquery'
       Description="Fleet osquery"
       InstallerVersion="500"
@@ -25,6 +24,8 @@ var windowsWixTemplate = template.Must(template.New("").Option("missingkey=error
       InstallPrivileges="elevated"
       Languages="1033" />
 
+    <Property Id="REINSTALLMODE" Value="amus" />
+
     <MediaTemplate EmbedCab="yes" />
 
     <MajorUpgrade AllowDowngrades="yes" />