Add utility functions for checking whether a process should be
considered privileged.

Add predicate function for checking whether dispatched dsme
message originates from privileged client (or dsme itself).

Make it possible to mark D-Bus method calls served by dsme as
privileged and send access denied error reply if such method
is called from an unpriviliged client.

Do not trigger vibration feedback when shutdown/reboot requests
are received, so that vibration occurs only when such requests
are accepted.

Move legacy aegis credential check delay in dsmetool so that it
happens on disconnect rather than on connect. While such delay
is not necessary anymore, having it occur just before exit allows
dsme side diagnostic logging to have access to client details.
Signed-off-by: Simo Piiroinen <simo.piiroinen@jolla.com>