BUILD: Properly expand variables in sssd-ifp.service

systemd[1]: [/usr/lib/systemd/system/sssd-ifp.service:9]
    Path '-@environment_file@' is not absolute, ignoring.

sh-4.2# systemctl cat sssd-ifp.service
 # /usr/lib/systemd/system/sssd-ifp.service
[Unit]
Description=SSSD IFP Service responder
Documentation=man:sssd-ifp(5)
After=sssd.service
BindsTo=sssd.service

[Service]
Environment=DEBUG_LOGGER=--logger=files
EnvironmentFile=-@environment_file@
Type=dbus
BusName=org.freedesktop.sssd.infopipe
ExecStart=/usr/libexec/sssd/sssd_ifp --uid 0 --gid 0 --dbus-activated ${DEBUG_LOGGER}

Resolves:
https://pagure.io/SSSD/sssd/issue/3433

Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>

Makefile.am

@@ -1491,7 +1491,7 @@ EXTRA_DIST += \
     src/responder/ifp/org.freedesktop.sssd.infopipe.service.in \
     $(NULL)
 
-ifp_edit_cmd = $(SED) \
+ifp_edit_cmd = $(edit_cmd) \
         -e 's|@ifp_exec_cmd[@]|$(ifp_exec_cmd)|g' \
         -e 's|@ifp_systemdservice[@]|$(ifp_systemdservice)|g' \
         -e 's|@ifp_restart[@]|$(ifp_restart)|g'