qemu-ga: Fixed minor version switch issue

With automatically generated GUID, on minor version changes, an error
occurred, stating that there is a problem with the installer.
Now, a notification is shown, warning the user that another version of
this product is already installed, and that configuration or removal of
the existing version is possible through Add/Remove Programs on the
Control Panel (expected behavior).

Signed-off-by: Leonid Bloch <leonid@daynix.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/installer/qemu-ga.wxs

@@ -41,7 +41,7 @@
 
   <Product
     Name="QEMU guest agent"
-    Id="*"
+    Id="{DF9974AD-E41A-4304-81AD-69AA8F299766}"
     UpgradeCode="{EB6B8302-C06E-4BEC-ADAC-932C68A3A98D}"
     Manufacturer="$(env.QEMU_GA_MANUFACTURER)"
     Version="$(env.QEMU_GA_VERSION)"