container/initoverlay: configure via fsconfig

This works around the page size limit at the cost of negligible performance regressions.

Closes #34.

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

container/dispatcher_test.go

@@ -468,6 +468,14 @@ func (k *kstub) mountTmpfs(fsname, target string, flags uintptr, size int, perm
 		stub.CheckArg(k.Stub, "perm", perm, 4))
 }
 
+func (k *kstub) mountOverlay(target string, options [][2]string) error {
+	k.Helper()
+	return k.Expects("mountOverlay").Error(
+		stub.CheckArg(k.Stub, "target", target, 0),
+		stub.CheckArgReflect(k.Stub, "options", options, 1),
+	)
+}
+
 func (k *kstub) ensureFile(name string, perm, pperm os.FileMode) error {
 	k.Helper()
 	return k.Expects("ensureFile").Error(