units: rework systemd-exit.service to terminate systemd via signal rather than bus

This should make session termination more reliable, as D-Bus doesn't
have to be around anymore for this to succeed.

Makefile.am

@@ -3613,6 +3613,7 @@ SED_PROCESS = \
 		-e 's,@rootprefix\@,$(rootprefix),g' \
 		-e 's,@udevlibexecdir\@,$(udevlibexecdir),g' \
 		-e 's,@sushell\@,$(sushell),g' \
+		-e 's,@KILL\@,$(KILL),g' \
 		-e 's,@QUOTAON\@,$(QUOTAON),g' \
 		-e 's,@QUOTACHECK\@,$(QUOTACHECK),g' \
 		-e 's,@SYSTEM_SYSVINIT_PATH\@,$(sysvinitdir),g' \

configure.ac

@@ -64,10 +64,12 @@ AC_PROG_GCC_TRADITIONAL
 AC_PATH_PROG([M4], [m4])
 AC_PATH_PROG([XSLTPROC], [xsltproc])
 
-AC_PATH_PROG([QUOTAON], [quotaon], [/sbin/quotaon])
-AC_PATH_PROG([QUOTACHECK], [quotacheck], [/sbin/quotacheck])
+AC_PATH_PROG([QUOTAON], [quotaon], [/usr/sbin/quotaon])
+AC_PATH_PROG([QUOTACHECK], [quotacheck], [/usr/sbin/quotacheck])
 
-AC_PATH_PROG([SETCAP], [setcap], [/sbin/setcap])
+AC_PATH_PROG([SETCAP], [setcap], [/usr/sbin/setcap])
+
+AC_PATH_PROG([KILL], [kill], [/usr/bin/cap])
 
 # gtkdocize greps for '^GTK_DOC_CHECK', so it needs to be on its own line
 m4_ifdef([GTK_DOC_CHECK], [

units/user/systemd-exit.service.in

@@ -14,4 +14,4 @@ After=shutdown.target
 
 [Service]
 Type=oneshot
-ExecStart=@SYSTEMCTL@ --user --force exit
+ExecStart=@KILL@ -s RTMAX-6 $MANAGERPID