Provide shell command to ease connections to complex scenarii

Summary:
For example, it allows to call a Docker container execution command
on a remote server through an interactive SSH connection:

shell devcentral = ssh -t dwellers.nasqueron.org docker exec -it bash
shell devcentral foo = ssh -t dwellers.nasqueron.org docker exec -it foo

Test Plan:
Python development

Checked with flake8 and autopep8.

Deployment test procedure

• salt-call --local state.apply roles/devserver/userland-software/misc
• shell devcentral

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1401