connman: fix missing dbus configuration files

Without connman.conf in /etc/dbus-1/system.d/, connmand cannot take
its name on the dbus system bus and will fail to start with a
permission denied error.

Signed-off-by: Mike Williams <mike@mikebwilliams.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>