Add an option to create a data bag from JSON data in a file.

An option --json-file is added that takes a file path.
I.e.

  $ knife solo data bag create my_bag my_item --json-file foo.json

The file's contents are loaded and used as the contents of the new
data bag.
Merge pull request #10 from joeyates/master

Add an option to create a data bag from JSON data in a file