ACRN: dm: Modify runC default rootfs directory

The patch changes runC container's default rootfs directory. In the patch
change the rootfs to runC bundle's parent directory. Because in ACRN we map
SOS rootfs to container so the rootfs is an empty directory, after move it to
parent directory all the container can share the same rootfs.

Tracked-On: #2020
Signed-off-by: Long Liu <long.liu@intel.com>
Reviewed-by: Yu Wang <yu1.wang@intel.com>

Author: liudlong

devicemodel/samples/apl-mrb/runC.json

@@ -224,7 +224,7 @@
 		}
 	},
 	"root": {
-		"path": "rootfs",
+		"path": "../rootfs",
 		"readonly": false
 	},
 	"hostname": "runc",