Help reduce system service hijacking.

  During an app install force all non-system
services with positive priority to 0. Competition
among equal priority services can lead to
hijacking certain system services because we
can't rely on the priority label being properly
enforced. That is, any app can register a service
with an arbitrarily large priority value. This
change is inline with similar changes already in
place for activities.

  Also, if multiple services with the same
priority resolve for a given intent then
ensure that system app services are considered
before non-system apps. This has the effect
of always choosing a system app service
component before a non system app service
component for a connection or binding attempt.

Change-Id: Id149905168f4a17b2708e26fc91e6b3a3446ef53
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>