Allow system_app to find all system services.

SystemPropPoker in settings app lists and communicates with every service on the
system on property change, which is not currently allowed for all services.

This occurs, for instance, when toggling
Developer options -> Monitoring -> Profile GPU Rendering -> On scren as bars.

Addresses the following denials:
SELinux : avc:  denied  { find } for service=samplingprofiler scontext=u:r:system_app:s0 tcontext=u:object_r:samplingprofiler_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=DockObserver scontext=u:r:system_app:s0 tcontext=u:object_r:DockObserver_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=devicestoragemonitor scontext=u:r:system_app:s0 tcontext=u:object_r:devicestoragemonitor_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=media.camera.proxy scontext=u:r:system_app:s0 tcontext=u:object_r:cameraproxy_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=scheduling_policy scontext=u:r:system_app:s0 tcontext=u:object_r:scheduling_policy_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=battery scontext=u:r:system_app:s0 tcontext=u:object_r:battery_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=processinfo scontext=u:r:system_app:s0 tcontext=u:object_r:processinfo_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=batteryproperties scontext=u:r:system_app:s0 tcontext=u:object_r:healthd_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=drm.drmManager scontext=u:r:system_app:s0 tcontext=u:object_r:drmserver_service:s0 tclass=service_manager
SELinux : avc:  denied  { find } for service=commontime_management scontext=u:r:system_app:s0 tcontext=u:object_r:commontime_management_service:s0 tclass=service_manager

Bug: 20762975
Bug: 21446739
Change-Id: I92b7629077eb5aabffb72170f4ef71f574ebb95c