Can I move the OS X that was preinstalled on my MacBook pro to a VM running on the MacBook Pro?
You could try to download the Yosemite installer (or another OSX version if your "purchased" it earlier) and try if you can install a virtual machine with it. You could also visit this link (it is for parallels, but maybe it will also work with virtual box): http://kb.parallels.com/en/118806