run-postinsts: propagate exit state to run-postinsts.service

run-postinsts: propagate exit state to run-postinsts.service

In case an exec_postinst_scriptlets child process fails during installation we
want indication that the run-postinsts.service had a problem.

We still try to install all scriptlets and only run remove_rcsd_link if all
postinst scripts ran without error. Otherwise on every following boot a new
install attempt of the missing scriptlet(s) is performed.

Signed-off-by: Bastian Germann <Bastian.Germann@duagon.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>