Allow PrintSpooler to see PrintServices

the print spooler is the print preview UI. It communicates with the
PrintServices (== printer drivers) through the system server. In some
cases (such as for icons) it communicates directly. Hence the
PrintSpooler needs to be able to see the PrintServices.

Test: Looked at UI and saw icons
Fixes: 149403662
Change-Id: I94d26439ca2586f1c45712647d838c3211652a8a