hst: optionally cover /run/ early

This works around awkward root permissions.

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

internal/outcome/shim_test.go

@@ -71,6 +71,7 @@ func TestShimEntrypoint(t *testing.T) {
 			Tmpfs(fhs.AbsDevShm, 0, 01777).
 
 			// spRuntimeOp
+			Tmpfs(fhs.AbsRun, xdgRuntimeDirSize, 0755).
 			Tmpfs(fhs.AbsRunUser, xdgRuntimeDirSize, 0755).
 			Bind(m("/tmp/hakurei.10/runtime/9999"), m("/run/user/1000"), std.BindWritable).