locked_version must be present for all items in Lockfile

It looks like we're dynamically determining the locked_version of cookbooks using special types of locations. I have confirmed this true for path, I'll have to check git and friends.

The locked_version must be provided to ensure that the lockfile is portable and can be distributed with a package of cookbooks for application at a later date. This goes hand in hand with #933.

@sethvargo was this originally done to just to avoid rewriting the lockfile each time the version of the cookbook was bumped?