Apply memory limit for openqa-worker services

All workers are already part of openqa-worker.slice, apply memory limit
to that slice to ensure that memory cannot be exhausted exclusively by
workers.

Reference: https://progress.opensuse.org/issues/133511

Makefile

@@ -99,7 +99,7 @@ install-generic:
 	install -d -m 755 "$(DESTDIR)"/usr/lib/systemd/system
 	install -d -m 755 "$(DESTDIR)"/usr/lib/systemd/system-generators
 	install -d -m 755 "$(DESTDIR)"/usr/lib/tmpfiles.d
-	for i in systemd/*.{service,target,timer,path}; do \
+	for i in systemd/*.{service,slice,target,timer,path}; do \
 		install -m 644 $$i "$(DESTDIR)"/usr/lib/systemd/system ;\
 	done
 	ln -s [email protected] "$(DESTDIR)"/usr/lib/systemd/system/[email protected]

dist/rpm/openQA.spec

@@ -693,6 +693,7 @@ fi
 %dir %{_unitdir}
 %{_systemdgeneratordir}
 %{_unitdir}/openqa-worker.target
+%{_unitdir}/openqa-worker.slice
 %{_unitdir}/[email protected]
 %{_unitdir}/[email protected]
 %{_unitdir}/openqa-worker-cacheservice-minion.service

systemd/openqa-worker.slice

@@ -0,0 +1,7 @@
+[Unit]
+Description=Slice for openqa-worker units
+
+[Slice]
+# Apply memory limit to this slice to ensure that memory cannot be exhausted
+# exclusively by openqa-worker services.
+MemoryMax=90%