test: Ensure delegation test unit has memory controller

When the test used to be run on distro that doesn't enable memory
accounting by default (such as openSUSE TW), there is no guarantee that
testing unit has memory.* cgroup attributes and delegation test would
fail if they are missing.

Require memory controller explicitly inside the unit so that test can
work in any environment.

test/units/TEST-19-CGROUP.delegate.sh

@@ -32,6 +32,7 @@ for attr in cgroup.threads memory.oom.group memory.reclaim ; do
     if grep -q "$attr" /sys/kernel/cgroup/delegate ; then
         systemd-run --wait \
                     --unit=test-0.service \
+                    --property="MemoryAccounting=1" \
                     --property="DynamicUser=1" \
                     --property="Delegate=" \
                     test -w /sys/fs/cgroup/system.slice/test-0.service/ -a \