Allow Barbican Objects to be Created via Json File

Problem Description
===================

Python-barbicanclient users may wish to input a `json_file` file path and have
a Barbican object generated from the file. Currently all the metadata of
a Barbican object must be passed through a series of parameters.

Proposed Change
===============

The proposed change will be to add a new argument to the Python-barbicanclient
CLI to allow for a `json_file` as an input. It will also allow the client to
be able to generate a Barbican object from a file. The passed file will go
through validation before a Barbican object is created.