Start bt-service with systemd user with multi-user option

Start bt-service with systemd user with multi-user option

In multi-user environment bt-service cannot be launch by dbus-activation or
systemd-dbus activation.

- Add bcond_with multi-user option
- Add MULTI_USER_SUPPORT build option
- Remove rc.d/init.d in multi-user environment because done with systemd
user and  bluetooth-frwk-service scprit is for app user.
- Change dbus policy for multi-user
- Fix systemd unit file Install section
- Fix TZPC-4380

Signed-off-by: Victor Hakoun <victor.hakoun@eurogiciel.fr>