Start role service earlier.

Role service is modularized in this release and allows lower level
roles to be introduced after role logic is moved from
PermissionController APK into the system server JAR. So move starting
role service earlier as well to allow lower level roles.

This has no immediate effect because currently initialization for all
roles happens upon user start, but once role logic is inside system
server, we can allows initializing certain roles earlier in the boot
process, e.g. via SystemService.onBootPhase().

Fixes: 178565325
Test: presubmit
Change-Id: I8d183553f08aa6200aa3566afaabd40a7ce9489c
(cherry picked from commit d9306019)