hst: optionally cover /run/ early

This works around awkward root permissions.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/outcome/run_test.go

@@ -136,6 +136,7 @@ func TestOutcomeRun(t *testing.T) {
 				Tmpfs(fhs.AbsDevShm, 0, 01777).
 
 				// spRuntimeOp
+				Tmpfs(fhs.AbsRun, xdgRuntimeDirSize, 0755).
 				Tmpfs(fhs.AbsRunUser, xdgRuntimeDirSize, 0755).
 				Bind(m("/tmp/hakurei.0/runtime/9"), m("/run/user/1971"), std.BindWritable).