afm-user-daemon: accept bus address with arguments

It might be necessary to pass the address as an argument because
library systemd uses secure_getenv to retrieves the default
addresses and secure_getenv might return NULL in some cases.

Change-Id: Iea14a0494f39875f0a501e53a2711b0df96bab3c
Signed-off-by: José Bollo <jose.bollo@iot.bzh>