checkpoint: resolve symlink for external bind mount

runc resolves symlink before doing bind mount. So
we should save original path while formatting CriuReq for
checkpoint.

Signed-off-by: Liu Hua <weldonliu@tencent.com>

tests/integration/checkpoint.bats

@@ -126,7 +126,18 @@ function simple_cr() {
 	done
 }
 
-@test "checkpoint and restore " {
+@test "checkpoint and restore" {
+	simple_cr
+}
+
+@test "checkpoint and restore (bind mount, destination is symlink)" {
+	mkdir -p rootfs/real/conf
+	ln -s /real/conf rootfs/conf
+	update_config '	  .mounts += [{
+					source: ".",
+					destination: "/conf",
+					options: ["bind"]
+				}]'
 	simple_cr
 }