af-main: report error status in afm-install

af-main: report error status in afm-install

The script afm-install wasn't able to report errors.
This patch suggested by Tadao Tanikawa ensure that
the status returned by dbus-send is reported to the
caller and solves the issue.

Bug-AGL: SPEC-699

Change-Id: Id9147794e534eeb9780ddfd4f4702becc87b2163
Signed-off-by: José Bollo <jose.bollo@iot.bzh>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/9799
Reviewed-by: Stéphane Desneux <stephane.desneux@iot.bzh>
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>