json-edit: Add ability to remove attributes
json-edit: Spacing fixes
json-edit: Fix setting/removing of some non-existing subattributes

If there's already an attribute like foo.bar set to "test", then it was
failing when trying to do something on the foo.bar.foo attribute.

Now, when setting, we overwrite foo.bar to be a hash, and when removing
we just exit early.
Merge pull request #1877 from vuntz/json-edit-improvements

Several improvements to json-edit tools (for pebbles, suse-only)