multi-user: Add multi-user support in service

multi-user: Add multi-user support in service

Use cases:

Given 2 users: UserA and UserB

1. If UserA is connected to a wifi service, then UserB is not allowed
to connect wifi service, and not allowed to disconnect the service
UserA connected.

2. If UserA is connected to a wifi service, then UserB is allowed to
use the same connection, but he is not allowed to modify the connection.

3. If UserA is connected to a wifi service with security wep/wpa/psk,
then UserA disconnects it, when UserB tries to connect the same wifi
service, it must input passphrase to connect it.

Change-Id: Id686ebd7d1f3490875a9d8f877219bd004907227