Test sge_execd in two steps

cluster/sge.enable.host.queue.sh

@@ -565,6 +565,11 @@ main() {                                                        # {{{
 			&& systemctl --quiet start sge_execd.service > /dev/null 2>&1 \
 			&& sleep "${sleep_delay}"
 		## }}}
+		## If anything related to SGE is still absent from the system {{{
+		### Exit with error if the service can't start
+		is_proc_absent "${sge_proc_pattern}" \
+			&& exit 4
+		## }}}
 	fi
 
 	## If we need to watch for upgrades