Add 'pulp-smash shell' command.

[rochacbruno]

$ pulp-smash shell --help      
Usage: pulp-smash shell [OPTIONS]

  Run a Python shell with Pulp-Smash context.

  Start an interactive shell with pulp-smash objects available, if `ipython`
  is installed it will start ipython session, else it will start standard
  python shell.

Options:
  --ipython / --no-ipython
  --help                    Show this message and exit.

$ pulp-smash shell       
Welcome to Pulp-Smash interactive shell
	Auto imported: api, cli, config, utils, pulp2, pulp3, constants, exceptions
	Available objects: api.client, cli.client, cfg

In [1]: api.client.get('/pulp/api/v2/status/').json()
Out[1]: 
{'known_workers': [{'_ns': 'workers',
   'last_heartbeat': '2019-03-20T18:44:57Z',
   '_id': 'scheduler@rhel-76-pulp-2'},
  {'_ns': 'workers',
   'last_heartbeat': '2019-03-20T18:44:57Z',
   '_id': 'resource_manager@rhel-76-pulp-2'},
  {'_ns': 'workers',
   'last_heartbeat': '2019-03-20T18:44:54Z',
   '_id': 'reserved_resource_worker-0@rhel-76-pulp-2'}],
 'messaging_connection': {'connected': True},
 'database_connection': {'connected': True},
 'api_version': '2',
 'versions': {'platform_version': '2.19c1'}}

[nixocio]

I like this idea. I will get back to this PR later.

[dralley]

Oh nice, that looks great!

[bherrin3]

That's awesome, but I think there is a subliminal message I should become vegan...

[ragabala]

💯

[nixocio]

@rochacbruno, I would suggest to add your section demo as part of the docs. Great work to be not used.